We thank David Meints, University of Arkansas for his assistance in developing and analyzing the transgenic maize during the early generations. This work received the financial support of USDA-ARS CRIS project 6054-42000-025-00D. Mention of trade names or commercial products in this article is solely for the purpose of providing specific information and does not imply recommendation or endorsement by the US Department of Agriculture. USDA-ARS&#8217; Equal Employment Opportunity (EEO) Policy mandates equal opportunity for all persons and prohibits discrimination in all aspects of the Agency&#8217;s personnel policies, practices, and operations.

1. Plasmid constructs and maize transformation
<ol>
	<li>PCR amplify Lablab AILP insert using the primers 5&#8217;-TATCTAGAACTAGTGATTACCATGGCTCC-3&#8217; and 5&#39;-ATACTGCAGGATTGCATGCAGAGTAGTACTG-3&#39;. The PCR conditions include an initial denaturation step at 98 &#176;C for 30 s (step 1), followed by denaturation at 98 &#176;C for 10 s (step 2), annealing at 55 &#176;C for 30 s (step 3), elongation at 72 &#176;C for 20 s (step 4), 31 cycles of step 2 to step 4, and a final elongation step at 72 &#176;C for 5 min. Clone the PCR product into a modified pCAMBIA 1,300 vector using XbaI and PstI restriction sites. Sequence the final plant destination vector to confirm the orientation and sequence of the cloned AILP gene in the vector.</li>
	<li>Transform Agrobacterium strain EHA101 with the final vector construct (Figure 1) as earlier described 16.</li>
	<li>Use transformed Agrobacterium containing the final plant destination vector to transform immature maize (Zea mays L. Hi-II) embryos (performed at the Plant Transformation Facility of Iowa State University) 16.</li>
	<li>Grow T0 plants in the greenhouse (26&#8211;29 &#176;C; 16/8 h photoperiod supplemented with High Pressure Na-lamps) and repeatedly self-pollinate to obtain T6 generation to achieve homozygosity for the transgenic trait.</li>
</ol>
2. Spore germination assay
<ol>
	<li>Harvest leaf samples and store at -80 &#176;C. Grind leaf samples with a mortar and pestle using liquid nitrogen. Weigh out 0.5 g in 2 mL microcentrifuge tubes, add 17 &#181;L of protease inhibitor, and place tubes on ice.</li>
	<li>Centrifuge tubes for 10 min at 16,000 x g. Transfer 225 &#181;L of plant extract to 0.5 mL microcentrifuge tubes and place on ice.</li>
	<li>In a 15 mL centrifuge tube, prepare a 5 mL spore suspension of Aspergillus flavus 70 &#8211; GFP in 1% potato dextrose broth (w/v). Vortex and adjust spore concentration to 105 spores/mL with a haemocytometer. 
	CAUTION: A. flavus produces aflatoxins, all work with this fungus should be conducted in a biological safety cabinet.</li>
	<li>Incubate in PDB at 28 &#176;C until culture achieves 50% initiation of spore germination as indicated by bulging of spores.</li>
	<li>Vortex and aliquot 25 &#181;L spore solution to the 225 &#181;L plant extract. Incubate samples for 20 hours at 28 &#176;C with intermittent shaking.</li>
	<li>Aliquot 25 &#181;L of spore solution on a microscope slide and measure the length of germ tubes spores using the digital camera software. Use a minimum of 20 replicate measurements for each line. 
	NOTE: At this stage, place all cultures at 4 &#176;C to stop colony growth until ready to count.</li>
</ol>
3. Kernel Screening Assay (KSA)
<ol>
	<li>Construct KSA caps by gluing 4 snap caps (22 mm) in a 60 x 15 mm petri dish. Allow glue to dry for 48 H before using caps. Each KSA cap constitutes one rep. (Figure 2).</li>
	<li>In a sterile biological safety cabinet, spray a square bioassay tray (24 cm x 24 cm) with 70% ethanol:H2O (v/v) and let air dry. Add sterile chromatography paper to the tray. Spray 9 KSA caps with 70% ethanol, let air dry, and place in the bioassay tray.</li>
	<li>For each transgenic maize line being tested, select 20 undamaged kernels and place in a 50 mL centrifuge tube. Add 70% ethanol and let sit for 4 minutes. Gently shake tubes during sterilization. Pour off the ethanol and rinse kernels three times in sterile deionized H2O.</li>
	<li>Prepare a spore suspension of Aspergillus flavus 70 &#8211; GFP17 from a 6 day old culture grown on V8 medium (5% V8 Juice, 2% agar, pH 5.2).
	<ol>
		<li>Add 20 mL sterile 0.02% Triton X-100/deionized H2O (v/v) and scrap off spores with a sterile loop. Pipet off the inoculum and place in a 300 mL sterile beaker.</li>
		<li>Prepare a 5-fold dilution with 0.02% Triton X-100, then perform a spore count with a haemocytometer. Dilute again if necessary to obtain 100 mL with a concentration of 4 x 106 spores/mL.</li>
	</ol>
	</li>
	<li>Place kernels in a sterile 300 mL beaker with a stir bar. Add inoculum to the beaker. 
	CAUTION: Adding kernels to inoculum will cause solution to splash. Place beaker on a stir plate for 3 minutes. After 3 minutes, pour off inoculum into an empty beaker.</li>
	<li>Using a forceps, place kernels in the bioassay dish (1 kernel/cap). Add 30 mL deionized water to the bottom of each bioassay tray and incubate at 31 &#176;C in the dark for 7 days.</li>
	<li>Prepare kernels for photography.
	<ol>
		<li>Set aside 4 kernels from each line for microscopic analysis and photography. 
		NOTE: Kernels can be stored at 4 &#176;C for no longer than 5 days before completing photography.</li>
		<li>Take pictures of kernels after seven days of inoculation with A. flavus (Figure 3).</li>
		<li>Clean exterior of kernels with a soft tissue and deionized water. Perform longitudinal sections of kernels and immediately take photographs under the fluorescent microscope.</li>
	</ol>
	</li>
	<li>Prepare kernels for analysis.
	<ol>
		<li>Clean exterior of remaining kernels with a soft tissue and deionized water.</li>
		<li>Place 4 kernels, constituting 1 rep, in a 15 mL screw cap polycarbonate vial containing 2 stainless steel balls. Immediately freeze vials in liquid nitrogen and store at -80 &#176;C until further processing and analysis.</li>
		<li>Remove vials from -80 &#176;C freezer and grind kernels in a homogenizer at 1,500 rpm for 3 minutes. 
		NOTE: Keep kernels frozen with liquid nitrogen.</li>
	</ol>
	</li>
</ol>
4. PCR screening of transgenic maize kernels
<ol>
	<li>Use DNA isolation kit to isolate genomic DNA (gDNA) from pulverized maize kernels infected with A. flavus according to the manufacturer&#8217;s instructions. Briefly, add 280 &#181;L buffer F, 20 &#181;L protease, and 3 &#181;L dithiothreitol (DTT) to 10-15 mg of pulverized maize kernels. Incubate and shake in a thermomixer (56 &#176;C, 1,200 rpm, 30 min). Centrifuge at 10,000 x g for 1 min and transfer the clear supernatant to equilibrated column. Incubate at room temperature for 3 min and centrifuge at 700 x g for 1 min to elute gDNA.</li>
	<li>Take 0.8 &#181;L of extracted gDNA to set up a 20 &#181;L PCR reaction for each sample using a PCR kit. Follow thermocycling conditions as recommended in the manufacturer&#8217;s protocol. The PCR conditions include an initial denaturation step at 98 &#176;C for 5 min (step 1) followed by denaturation at 98 &#176;C for 5 s (step 2), annealing at 55 &#176;C for 5 s (step 3), elongation at 72 &#176;C for 20 s (step 4), 40 cycles of step 2 to step 4, and a final elongation step at 72 &#176;C for 1 min (step 5).</li>
	<li>Use forward primer 5&#8217;-TATACCACCCCCATCCGTGT-3&#8217; and reverse primer 5&#8217;-AGCTCGGAAGCAAAAGACCA-3&#8217; to confirm the presence of the Lablab AILP gene in the transgenic maize kernels.</li>
</ol>
5. RNA isolation, cDNA synthesis, and semi-quantitative RT-PCR
<ol>
	<li>Take homogenized A. flavus infected maize kernels previously stored at -80&#176;C for RNA extraction. Extract RNA using a total RNA isolation kit according to the manufacturer&#8217;s protocol but with slight modification18. After adding 50 mg of homogenized maize kernel powder in the extraction buffer, mix it well (without vortexing) using a 1 mL pipet tip and leave it on ice for 5-6 minutes before proceeding to subsequent steps as described in the manufacturer&#8217;s protocol.</li>
	<li>Prepare cDNA using a cDNA synthesis kit according to the manufacturer&#8217;s protocol 18.</li>
	<li>Use 0.5 &#181;L of undiluted cDNA per PCR reaction for semi-quantitative RT-PCR as earlier described18. Use forward and reverse primers qAILP-F 5&#8217;-TCCCAACAAGGCAACTACTG-3&#8217; and qAILP-R 5&#8217;- CGGTGTCGAAGAGACCTAGATA-3&#8217; respectively to detect Lablab AILP gene expression, and forward and reverse primers qRib-F 5&#697;-GGCTTGGCTTAAAGGAAGGT-3&#697; and qRib-R 5&#697;-TCAGTCCAACTTCCAGAATGG-3&#697; respectively for expression of maize ribosomal structural gene (Rib), GRMZM2G02483819 as a house-keeping gene.</li>
</ol>
6. GFP quantitation
<ol>
	<li>Prepare 50 mL each of 0.2 M monobasic sodium phosphate (NaH2PO4) and 0.2 M dibasic sodium phosphate (Na2HPO4&#183;7H2O) in deionized H2O.</li>
	<li>Make up 100 mL of pH 7.0 Sorenson&#8217;s phosphate buffer. For pH 7.0, add 19.5 mL NaH2PO4 stock, 30.5 mL NaHPO4&#183;7H2O stock, and 50 mL deionized H2O.</li>
	<li>Weigh out 25 mg ground kernel material (fresh weight, FW) and place in a 1.0 mL microcentrifuge tube. Add 500 &#181;L phosphate buffer to the centrifuge tube and vortex for 30 s.</li>
	<li>Centrifuge samples for 15 minutes at 16,000 x g. Pipet 100 &#181;L supernatant into a black 96 well plate. Read the samples with a fluorometer (excitation 485 nm, emission 528 nm).</li>
</ol>
7. Total aflatoxin analysis
<ol>
	<li>Sample processing and aflatoxin extraction
	<ol>
		<li>Dry kernel samples in a forced air oven for 2 days at 60 &#176;C. Weigh samples and place in a 50 mL Erlenmeyer flask with a glass stopper.</li>
		<li>In a fume hood, add 25 mL methylene chloride to each flask. 
		CAUTION: Methylene chloride is highly volatile and is considered hazardous (irritant, carcinogen).&#160;Neither latex nor nitrile gloves are safe for working with Methylene Chloride. Use IMPROVED organic solvent resistant PolyVinylAlcohol gloves.</li>
		<li>Shake samples for 30 min on a wrist action shaker. After 30 min, slowly pour the extract through a fluted filter paper circle into an 80 mL beaker. Let the beakers dry overnight in a fume hood.</li>
		<li>The next day, squirt methylene chloride (approximately 5 mL) around the inside rim of the dry beakers, swirl around, and pour into 2 dram glass vials. Leave vials open to dry in a fume hood overnight.</li>
	</ol>
	</li>
	<li>Aflatoxin analysis
	<ol>
		<li>Add 4.0 mL 80% methanol:deionized H2O (v/v) to vials.</li>
		<li>Use an aflatoxin extraction kit to filter purify methanol solution with the provided column. Analyze total aflatoxin levels with a fluorometer, according to the manufacturer&#8217;s instructions.</li>
	</ol>
	</li>
</ol>

<ol>
	<li>Ismaiel, A., Papenbrock, J. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Mycotoxins:+Producing+fungi+and+mechanisms+of+phytotoxicity.">Mycotoxins: Producing fungi and mechanisms of phytotoxicity.</a> Agriculture. 5 (3), 492-537 (2015).</li><li>Mitchell, N., Bowers, E., Hurburgh, C., Wu, F. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Potential+economic+losses+to+the+USA+corn+industry+from+aflatoxin+contamination.">Potential economic losses to the USA corn industry from aflatoxin contamination.</a> Food Additives &amp; Contaminants: Part A. 33 (3), 540-550 (2016).</li><li>Umesha, S., Manukumar, H. M., Chandrasekhar, B., Shivakumara, P., Shiva Kumar, J., Raghava, S., Avinash, P., Shirin, M., Bharathi, T. R., Rajini, S. B., Nandhini, M., Vinaya Rani, G., Shobha, M., Prakash, H. S. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Aflatoxins+and+food+pathogens:+Impact+of+biologically+active+aflatoxins+and+their+control+strategies.">Aflatoxins and food pathogens: Impact of biologically active aflatoxins and their control strategies.</a> Journal of the Science of Food and Agriculture. , (2016).</li><li>Brown, R. L., Menkir, A., Chen, Z. Y., Bhatnagar, D., Yu, J., Yao, H., Cleveland, T. E. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Breeding+aflatoxin-resistant+maize+lines+using+recent+advances+in+technologies+-+a+review.">Breeding aflatoxin-resistant maize lines using recent advances in technologies - a review.</a> Food Additives &amp; Contaminants - Part A Chemistry, Analysis, Control, Exposure &amp; Risk Assessment. 30 (8), 1382-1391 (2013).</li><li>Abbas, H., Accinelli, C., Shier, W. T. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Biological+control+of+aflatoxin+contamination+in+U.S.+crops+and+the+use+of+bioplastic+formulations+of+Aspergillus+flavus+biocontrol+strains+to+optimize+application+strategies.">Biological control of aflatoxin contamination in U.S. crops and the use of bioplastic formulations of Aspergillus flavus biocontrol strains to optimize application strategies.</a> Journal of Agricultural and Food Chemistry. 65, 7081-7087 (2017).</li><li>Udomkun, P., Wiredu, A. N., Nagle, M., M&#252;ller, J., Vanlauwe, B., Bandyopadhyay, R. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Innovative+technologies+to+manage+aflatoxins+in+foods+and+feeds+and+the+profitability+of+application+&#8211;+A+review.">Innovative technologies to manage aflatoxins in foods and feeds and the profitability of application &#8211; A review.</a> Food Control. 76, 127-138 (2017).</li><li>Dohroo, N. P., Bhardwaj, S. S., Shyram, K. R. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Amylase+and+invertase+activity+as+influenced+by+Pythium+pleroticum+causing+rhizome+rot+of+ginger.">Amylase and invertase activity as influenced by Pythium pleroticum causing rhizome rot of ginger.</a> Plant Disease Research. 2, 106-107 (1987).</li><li>Singh, R., Saxena, V. S., Singh, R. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Pectinolytic,+cellulolytic,+amylase+and+protease+production+by+three+isolates+of+Fusarium+solani+variable+in+their+virulence.">Pectinolytic, cellulolytic, amylase and protease production by three isolates of Fusarium solani variable in their virulence.</a> Indian Journal of Mycology and Plant Pathology. 19, 22-29 (1989).</li><li>Fakhoury, A. M., Woloshuk, C. P. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Amy1,+the+&#945;-amylase+gene+of+Aspergillus+flavus:+Involvement+in+aflatoxin+biosynthesis+in+maize+kernels.">Amy1, the &#945;-amylase gene of Aspergillus flavus: Involvement in aflatoxin biosynthesis in maize kernels.</a> Phytopathology. 89 (10), 908-914 (1999).</li><li>Bluhm, B. H., Woloshuk, C. P. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Amylopectin+induces+Fumonisin+B1+production+by+Fusarium+verticillioides+during+colonization+of+maize+kernels.">Amylopectin induces Fumonisin B1 production by Fusarium verticillioides during colonization of maize kernels.</a> Molecular Plant-Microbe Interactions. 18 (12), 1333-1339 (2005).</li><li>Gilbert, M. K., Majumdar, R., Rajasekaran, K., Chen, Z. Y., Wei, Q., Sickler, C. M., Lebar, M. D., Cary, J. W., Frame, B. R., Wang, K. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=RNA+interference-based+silencing+of+the+a-amylase+(amy1)+gene+in+Aspergillus+flavus+decreases+fungal+growth+and+aflatoxin+production+in+maize+kernels.">RNA interference-based silencing of the a-amylase (amy1) gene in Aspergillus flavus decreases fungal growth and aflatoxin production in maize kernels.</a> Planta. 247 (6), 1465-1473 (2018).</li><li>Chen, Z. Y., Brown, R. L., Russin, J. S., Lax, A. R., Cleveland, T. E. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=A+corn+trypsin+inhibitor+with+antifungal+activity+inhibits+Aspergillus+flavus+&#945;-amylase.">A corn trypsin inhibitor with antifungal activity inhibits Aspergillus flavus &#945;-amylase.</a> Phytopathology. 89 (18944733), 902-907 (1999).</li><li>Fakhoury, A. M., Woloshuk, C. P. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Inhibition+of+growth+of+Aspergillus+flavus+and+fungal+&#945;-amylases+by+a+lectin-like+protein+from+Lablab+purpureus.">Inhibition of growth of Aspergillus flavus and fungal &#945;-amylases by a lectin-like protein from Lablab purpureus.</a> Molecular Plant-Microbe Interactions. 14 (8), 955-961 (2001).</li><li>Mirkov, T. E., Wahlstrom, J. M., Hagiwara, K., Finardi-Filho, F., Kjemtrup, S., Chrispeels, M. J. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Evolutionary+relationships+among+proteins+in+the+phytohemagglutinin-arcelin-a-amylase+inhibitor+family+of+the+common+bean+and+its+relatives.">Evolutionary relationships among proteins in the phytohemagglutinin-arcelin-a-amylase inhibitor family of the common bean and its relatives.</a> Plant Molecular Biology. 26 (4), 1103-1113 (1994).</li><li>Kim, Y. H., Woloshuk, C. P., Cho, E. H., Bae, J. M., Song, Y. S., Huh, G. H. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Cloning+and+functional+expression+of+the+gene+encoding+an+inhibitor+against+Aspergillus+flavus+a-amylase,+a+novel+seed+lectin+from+Lablab+purpureus+(Dolichos+lablab).">Cloning and functional expression of the gene encoding an inhibitor against Aspergillus flavus a-amylase, a novel seed lectin from Lablab purpureus (Dolichos lablab).</a> Plant Cell Reports. 26 (4), 395-405 (2007).</li><li>Frame, B., Main, M., Schick, R., Wang, K., Thorpe, T. A., Yeung, E. C. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Ch.+22.">Ch. 22.</a> Plant Embryo Culture. 710, 327-341 (2011).</li><li>Rajasekaran, K., Sickler, C. M., Brown, R. L., Cary, J. W., Bhatnagar, D. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Evaluation+of+resistance+to+aflatoxin+contamination+in+kernels+of+maize+genotypes+using+a+GFP-expressing+Aspergillus+flavus+strain.">Evaluation of resistance to aflatoxin contamination in kernels of maize genotypes using a GFP-expressing Aspergillus flavus strain.</a> World Mycotoxin Journal. 6 (2), 151-158 (2013).</li><li>Rajasekaran, K., Sayler, R. J., Sickler, C. M., Majumdar, R., Jaynes, J. M., Cary, J. W. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Control+of+Aspergillus+flavus+growth+and+aflatoxin+production+in+transgenic+maize+kernels+expressing+a+tachyplesin-derived+synthetic+peptide,+AGM182.">Control of Aspergillus flavus growth and aflatoxin production in transgenic maize kernels expressing a tachyplesin-derived synthetic peptide, AGM182.</a> Plant Science. , 150-156 (2018).</li><li>Shu, X., Livingston, D. P., Franks, R. G., Boston, R. S., Woloshuk, C. P., Payne, G. A. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Tissue-specific+gene+expression+in+maize+seeds+during+colonization+by+Aspergillus+flavus+and+Fusarium+verticillioides.">Tissue-specific gene expression in maize seeds during colonization by Aspergillus flavus and Fusarium verticillioides.</a> Molecular Plant Pathology. 16 (4), 662-674 (2015).</li><li>Savary, S., Ficke, A., Aubertot, J. -. N., Hollier, C. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Crop+losses+due+to+diseases+and+their+implications+for+global+food+production+losses+and+food+security.">Crop losses due to diseases and their implications for global food production losses and food security.</a> Food Security. 4, 519-537 (2012).</li><li>Damalas, C. A., Eleftherohorinos, I. G. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Pesticide+exposure,+safety+issues,+and+risk+assessment+indicators.">Pesticide exposure, safety issues, and risk assessment indicators.</a> International Journal of Environmental Research and Public Health. 8 (5), 1402-1419 (2011).</li><li>Kowalska, A., Walkiewicz, K., Kozie&#322;, P., Muc-Wierzgo&#324;, M. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Aflatoxins:+Characterisitcs+and+impact+on+human+health.">Aflatoxins: Characterisitcs and impact on human health.</a> Post&#281;py Higieny i Medycyny Do&#347;wiadczalnej (Online). 71, 315-327 (2017).</li><li>Rajasekaran, K., Cary, J. W., Cotty, P. J., Cleveland, T. E. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Development+of+a+GFP-expressing+Aspergillus+flavus+strain+to+study+fungal+invasion,+colonization,+and+resistance+in+cottonseed.">Development of a GFP-expressing Aspergillus flavus strain to study fungal invasion, colonization, and resistance in cottonseed.</a> Mycopathologia. 165 (2), 89-97 (2008).</li><li>Punt, P., Dingemanse, M. A., Kuyvenhoven, A., Soede, R. D., Pouwels, P. H., van den Hondel, C. A. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Functional+elements+in+the+promoter+region+of+the+Aspergillus+nidulans+gpdA+gene+encoding+glyceraldehyde-3-phosphate+dehydrogenase.">Functional elements in the promoter region of the Aspergillus nidulans gpdA gene encoding glyceraldehyde-3-phosphate dehydrogenase.</a> Gene. 93 (1), 101-109 (1990).</li><li>Lee, L. W., Chiou, C. H., Klomparens, K. L., Cary, J. W., Linz, J. E. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Subcellular+localization+of+aflatoxin+biosynthetic+enzymes+Nor-1,+Ver-1,+and+OmtA+in+time-dependent+fractionated+colonies+of+Aspergillus+parasiticus.">Subcellular localization of aflatoxin biosynthetic enzymes Nor-1, Ver-1, and OmtA in time-dependent fractionated colonies of Aspergillus parasiticus.</a> Archives of Microbiology. 181 (3), 204-214 (2004).</li><li>Bhatnagar, D., Cary, J. W., Ehrlich, K., Yu, J., Cleveland, T. E. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Understanding+the+genetics+of+regulation+of+aflatoxin+production+and+Aspergillus+flavus+development.">Understanding the genetics of regulation of aflatoxin production and Aspergillus flavus development.</a> Mycopathologia. 162, 155-166 (2006).</li><li>Williams, W. P., Krakowsky, M. D., Scully, B. T., Brown, R. L., Menkir, A., Warburton, M. L., Windham, G. L. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Identifying+and+developing+maize+germplasm+with+resistance+to+accumulation+of+aflatoxins.">Identifying and developing maize germplasm with resistance to accumulation of aflatoxins.</a> World Mycotoxin Journal. 8 (2), 193-209 (2015).</li><li>Broekaert, W. F., van Parijs, J., Leyns, F., Joos, H., Peumans, W. J. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=A+chitin-binding+lectin+from+stinging+nettle+rhizomes+with+antifungal+properties.">A chitin-binding lectin from stinging nettle rhizomes with antifungal properties.</a> Science. 245 (4922), 1100-1102 (1989).</li><li>Vanparijs, J., Broekaert, W. F., Goldstein, I. J., Peumans, W. J. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Hevein-an+antifungal+protein+from+rubber-tree+(Hevea+brasiliensis)+latex.">Hevein-an antifungal protein from rubber-tree (Hevea brasiliensis) latex.</a> Planta. 183, 258-264 (1991).</li><li>Gozia, O., Ciopraga, J., Bentia, T., Lungu, M., Zamfirescu, I., Tudor, R., Roseanu, A., Nitu, F. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Antifungal+properties+of+lectin+and+new+chitinases+from+potato+tubers.">Antifungal properties of lectin and new chitinases from potato tubers.</a> Comptes Rendus de l'Academie des Sciences - Series III. 316 (8), 788-792 (1993).</li><li>Wisessing, A., Choowongkomon, K. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Amylase+inhibitors+in+plants:+Structures,+Functions+and+Applications.">Amylase inhibitors in plants: Structures, Functions and Applications.</a> Functional Plant Science and Biotechnology. 6 (1), 31-41 (2012).</li><li>Tyagi, B., Trivedi, N., Dubey, A. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=a-amylase+inhibitor:+A+compelling+plant+defense+mechanism+against+insect/pests.">a-amylase inhibitor: A compelling plant defense mechanism against insect/pests.</a> Environment &amp; Ecology. 32 (3), 995-999 (2014).</li><li>Powers, J. R., Culbertson, J. D. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=In+vitro+effect+of+bean+amylase+inhibitor+on+insect+amylases.">In vitro effect of bean amylase inhibitor on insect amylases.</a> Journal of Food Protection. 45, 655-657 (1982).</li><li>Gatehouse, A. M. R., Fenton, K. A., Jepson, I., Pavey, D. J. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=The+effects+of+a-amylase+inhibitors+on+insect+storage+pests:+Inhibition+of+a-amylase+in+vitro+and+effects+on+development+in+vivo.">The effects of a-amylase inhibitors on insect storage pests: Inhibition of a-amylase in vitro and effects on development in vivo.</a> Journal of the Science of Food and Agriculture. 37, 727-734 (1986).</li><li>Blanco-Labra, A., Chagolla-Lopez, A., Martinez-Gallardo, N., Valdes-Rodriguez, S. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Further+characterization+of+the+12-kDa+protease+a-amylase+inhibitor+present+in+maize+seeds.">Further characterization of the 12-kDa protease a-amylase inhibitor present in maize seeds.</a> Journal of Food Biochemistry. 19, 27-41 (1995).</li><li>Abdollahi, A., Buchanan, R. L. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Regulation+of+aflatoxin+biosynthesis:+Induction+of+aflatoxin+production+by+various+carbohydrates.">Regulation of aflatoxin biosynthesis: Induction of aflatoxin production by various carbohydrates.</a> Journal of Food Science. 46, 633-635 (1981).</li><li>Liu, J., Sun, L., Zhang, N., Zhang, J., Guo, J., Li, C., Rajput, S. A., Qi, D. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Effects+of+nutrients+in+substrates+of+different+grains+on+aflatoxin+B1+production+by+Aspergillus+flavus.">Effects of nutrients in substrates of different grains on aflatoxin B1 production by Aspergillus flavus.</a> BioMed Research International. 2016, (2016).</li><li>Uppala, S. S., Bowen, K. L., Woods, F. M. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Pre-harvest+aflatoxin+contamination+and+soluble+sugars+of+peanut.">Pre-harvest aflatoxin contamination and soluble sugars of peanut.</a> Peanut Science. 40 (1), 40-51 (2013).</li></ol>

The authors have no conflict of interest.

Yield losses in agricultural crops due to pathogens and pests is a global problem20. Currently, application of synthetic fungicides and pesticides is the predominant means for controlling plant pathogens and pests, but residual toxicity of these biochemicals in food and feed can pose serious threat to human and animal health21. Considering the economic importance of maize as a food and feed crop, reduction in or elimination of aflatoxin contamination is of utmost importance...

Mycotoxin contamination by the fungal genera, Aspergillus, Fusarium, Penicillium, and Alternaria is a major problem of food and feed crops grown worldwide1,2,3. Among these phytopathogenic fungi, Aspergillus has the highest adverse impact on crop value and human and animal health. Aspergillus flavus (A. flavus) is an opportunistic plant pathogen that infects oil rich crops such as maize, cottonseed and peanut and produces the potent carcinogens, aflatoxins, as well as numerous toxic secondary metabolites (SMs). Maize is an important food and feed crop grown worldwide and is highly susceptible to contamination by A. flavus. The economic impact of aflatoxin contamination on loses and reduced value in maize can be as much as $686.6 million/year in the U.S.2 With predicted changes in global climate, the impact of aflatoxins could result in greater economic losses in maize with estimates as high as $1.68 billion/year in the near future2. Given the adverse economic and health effects of aflatoxins in humans and livestock, pre-harvest aflatoxin control in maize might be the most efficient way to prevent aflatoxin contamination in food and feed products.
The major pre-harvest control approach for aflatoxin resistance in maize that has been used extensively in the last few decades is primarily through breeding, which requires a significant amount of time4. Recently, biocontrol has had some success in aflatoxin reduction in large scale field applications5,6. Besides biocontrol, application of cutting-edge molecular tools such as &#8216;Host Induced Gene Silencing&#8217; (HIGS) through RNAi and transgenic expression of resistance-associated proteins has had some success in reduction of A. flavus growth and aflatoxin production in small scale laboratory and field studies. These approaches are currently being optimized in addition to identifying new potential A. flavus gene targets for future manipulation.
Besides genes that are directly involved in mycotoxin production as potential targets of transgenic control strategies, fungal amylases have been shown to play a critical role in maintaining successful pathogenesis and mycotoxin production during early stages of host plant infection. A few examples include Pythium pleroticum (causal agent of ginger rhizome rot), Fusarium solani (causal agent of cauliflower wilt), where positive correlations between pathogenicity and &#945;-amylase expression and activity were observed7,8. Inhibition of &#945;-amylase activity either through gene knockout or knockdown approaches negatively affects fungal growth and toxin production. An &#945;-amylase knockout mutant of A. flavus was unable to produce aflatoxins when grown on starch substrate or degermed maize kernels9. Similarly, in Fusarium verticillioides an &#945;-amylase knockout strain failed to produce fumonisin B1 (mycotoxin) during infection of maize kernels10. In a more recent study, Gilbert et al. (2018) demonstrated that an RNAi-based knock down of A. flavus &#945;-amylase expression through HIGS significantly reduced A. flavus growth and aflatoxin production during maize kernel infection11.
Specific inhibitors of &#945;-amylase activity have also produced similar results as obtained from down-regulation of &#945;-amylase expression. The first report on the role of an &#945;-amylase inhibitor in fungal resistance came from the isolation and characterization of a 14-kDa trypsin-&#945;-amylase inhibitor from maize lines resistant to A. flavus12. Further screening of several hundreds of plant species by Fakhoury and Woloshuk led to the identification of a 36-kDa &#945;-amylase inhibitor-like protein (AILP) from the seeds of hyacinth beans, Lablab purpureus L.13. The peptide sequence of AILP resembled lectins belonging to the lectin&#8211;arcelin&#8211;&#945;-amylase inhibitor family reported in common bean14,15. Purified AILP does not exhibit any inhibitory activity towards mammalian trypsin and further in vitro characterization showed significant inhibition of A. flavus growth and conidial germination13. The reports presented here clearly shows &#945;-amylase can serve as a target in control approaches to restrict pathogens or pests that depend on starch mobilization (through &#945;-amylase activity) and acquisition of soluble sugars as an energy source during their pathogenic interaction with host plants.
Alpha-amylase is known to be critical in A. flavus pathogenicity9,10,11, and given the importance of AILP as a potent anti-A. flavus agent (&#945;-amylase inhibition/antigrowth)13, we generated transgenic maize plants expressing Lablab AILP gene under the constitutive CaMV 35S promoter. The goal was to investigate if heterologous expression of this &#945;-amylase inhibitor in maize is effective against A. flavus pathogenesis and aflatoxin production during maize kernel infection. Our results demonstrate that transgenic maize kernels expressing AILP significantly reduced A. flavus growth and aflatoxin production during kernel infection.

<table><tbody><tr><td>Agar</td><td>Caisson</td><td></td><td></td></tr><tr><td>Amazing Marine Goop</td><td>Eclectic Products</td><td></td><td></td></tr><tr><td>C1000 Touch CFX96 Real-Time System</td><td>Bio-Rad</td><td></td><td></td></tr><tr><td>Corning&amp;nbsp;Falcon Tissue Culture Dishes, 60 mm</td><td>Fisher Scientific</td><td>08-772F</td><td></td></tr><tr><td>Eppendorf&amp;nbsp;5424 Microcentrifuge</td><td>Fisher Scientific</td><td></td><td></td></tr><tr><td>Erlenmeyer flask with stopper, 50 mL</td><td>Ace Glass</td><td>6999-10</td><td></td></tr><tr><td>Ethanol</td><td></td><td></td><td></td></tr><tr><td>FluoroQuant Afla</td><td>Romer Labs</td><td>COKFA1010</td><td></td></tr><tr><td>Fluted Qualitative Filter Paper Circles, 15 cm</td><td>Fisher Scientific</td><td>09-790-14E</td><td></td></tr><tr><td>Force Air Oven</td><td>VWR</td><td></td><td></td></tr><tr><td>FQ-Reader</td><td>Romer Labs</td><td>EQFFM3010</td><td></td></tr><tr><td>Geno/Grinder 2010</td><td>OPS Diagnostics</td><td>SP 2010-115</td><td></td></tr><tr><td>Improved PolyVinylAlcohol Organic Solvent Resistant Gloves</td><td>Ansell</td><td>012-15-554</td><td></td></tr><tr><td>Innova 44 Incubator Shaker</td><td>Brunswick Scientific</td><td></td><td></td></tr><tr><td>iScript cDNA Synthesis Kit</td><td>Bio-Rad</td><td>1708890</td><td></td></tr><tr><td>liquid Nitrogen</td><td></td><td></td><td></td></tr><tr><td>Low Form Griffin Beakers, 100 mL</td><td>DKW Life Sciences</td><td>14000-100</td><td></td></tr><tr><td>Methanol</td><td></td><td></td><td></td></tr><tr><td>Methylene Chloride</td><td></td><td></td><td></td></tr><tr><td>Nexttec 1-step DNA Isolation Kit for Plants</td><td>Nexttec</td><td>47N</td><td></td></tr><tr><td>Nikon Eclipse E600 microscope with Nikon DS-Qi1 camera</td><td>Nikon</td><td></td><td></td></tr><tr><td>Nikon SMZ25 stereomicroscope with C-HGFI Episcopic Illuminator and Andor Zyla 4.2 sCMOS camera</td><td>Nikon</td><td></td><td></td></tr><tr><td>Nunc Square BioAssay Dishes</td><td>ThermoFisher Scientific</td><td>240835</td><td></td></tr><tr><td>Phire Plant Direct PCR Kit</td><td>ThermoFisher Scientific</td><td>F130WH</td><td></td></tr><tr><td>Polycarbonate Vials, 15 ml</td><td>OPS Diagnostics</td><td>PCRV 15-100-23</td><td></td></tr><tr><td>Potato Dextrose Broth</td><td></td><td></td><td></td></tr><tr><td>Snap Cap, 22 mm</td><td>DKW Life Sciences</td><td>242612</td><td></td></tr><tr><td>Sodium Phosphate dibasic heptahydrate</td><td>Sigma-Aldrich</td><td></td><td></td></tr><tr><td>Sodium Phosphate monobasic</td><td>Sigma-Aldrich</td><td></td><td></td></tr><tr><td>Spectrum Plant Total RNA Kit</td><td>Sigma-Aldrich</td><td>STRN50</td><td></td></tr><tr><td>Stainless Steel Grinding Balls, 3/8&#039;&#039;</td><td>OPS Diagnostics</td><td>GBSS 375-1000-02</td><td></td></tr><tr><td>Stir Plate</td><td></td><td></td><td></td></tr><tr><td>Synergy 4 Fluorometer</td><td>Biotek</td><td></td><td></td></tr><tr><td>T100 Thermal Cycler</td><td>Bio-Rad</td><td></td><td></td></tr><tr><td>Triton X-100</td><td>Sigma-Aldrich</td><td>T-9284</td><td></td></tr><tr><td>V8 juice</td><td>Campbell&#039;s</td><td></td><td></td></tr><tr><td>Whatman Qualitative Grade Plain Sheets, Grade 3</td><td>Fisher Scientific</td><td>09-820P</td><td></td></tr><tr><td>Wrist-Action Shaker</td><td>Burrell Scientific</td><td></td><td></td></tr></tbody></table>

inhibition of aspergillus flavus growth and aflatoxin production in transgenic maize expressing the &#945;-amylase inhibitor from lablab purpureus l.

Aflatoxin contamination in food and feed crops is a major challenge worldwide. Aflatoxins, produced by the fungus Aspergillus flavus (A. flavus) are potent carcinogens that substantially reduce crop value in maize and other oil rich crops like peanut besides posing serious threat to human and animal health. Different approaches, including traditional breeding, transgenic expression of resistance associated proteins, and RNA interference (RNAi)-based host-induced gene silencing of critical A. flavus gene targets, are being evaluated to increase aflatoxin resistance in susceptible crops. Past studies have shown an important role of &#945;-amylase in A. flavus pathogenesis and aflatoxin production, suggesting this gene/enzyme is a potential target to reduce both A. flavus growth and aflatoxin production. In this regard, the current study was undertaken to evaluate heterologous expression (under control of the constitutive CaMV 35S promoter) of a Lablab purpureus L. &#945;-amylase inhibitor-like protein (AILP) in maize against A. flavus. AILP is a 36-kDa protein, which is a competitive inhibitor of A. flavus &#945;-amylase enzyme and belongs to the lectin&#8211;arcelin&#8211;&#945;-amylase inhibitor protein family in common bean. In vitro studies prior to the current work had demonstrated the role of AILP in inhibition of A. flavus &#945;-amylase activity and fungal growth. Fungal growth and aflatoxin production in mature kernels were monitored in real time using a GFP-expressing A. flavus strain. This kernel screening assay (KSA) is very simple to set up and provides reliable and reproducible data on infection and the extent of spread that could be quantified for evaluation of germplasm and transgenic lines. The fluorescence from the GFP strain is closely correlated to fungal growth and, by extension, it is well-correlated to aflatoxin values.&#160; The goal of the current work was to implement this previous knowledge in a commercially important crop like maize to increase aflatoxin resistance. Our results show a 35%&#8211;72% reduction in A. flavus growth in AILP-expressing transgenic maize kernels which, in turn, translated into a 62%&#8211;88% reduction in aflatoxin levels.

Maize transformation and molecular screening of transgenic plants
Immature embryos of maize Hi-II lines were transformed using Agrobacterium tumefaciens EHA101 strain containing the final plant destination vector expressing the Lablab purpureus AILP gene under the control of CaMV 35S promoter. Five independently transformed maize lines were advanced to the T6 generation for su...

Watch this Scientific Journal Video about Inhibition of Aspergillus flavus Growth and Aflatoxin Production in Transgenic Maize Expressing the Î±-amylase Inhibitor from Lablab purpureus L. at JoVE.co

Inhibition of Aspergillus flavus Growth and Aflatoxin Production in Transgenic Maize Expressing the &#945;-amylase Inhibitor from Lablab purpureus L.

Here we present a protocol to analyze Aspergillus flavus growth and aflatoxin production in maize kernels expressing an antifungal protein.&#160; Using a GFP-expressing A. flavus strain we monitored the infection and spread of the fungus in mature kernels in real time. The assay is rapid, reliable, and reproducible.

Inhibition of Aspergillus flavus Growth and Aflatoxin Production in Transgenic Maize Expressing the &#945;-amylase Inhibitor from Lablab purpureus L.

Aflatoxin contamination in food and feed crops is a major challenge worldwide. Aflatoxins, produced by the fungus Aspergillus flavus (A. flavus) are ...

inhibition-aspergillus-flavus-growth-aflatoxin-production-transgenic

Research

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Environment

10.4K Views.  USDA-ARS, Food and Feed Safety Research Unit. Here we present a protocol to analyze Aspergillus flavus growth and aflatoxin production in maize kernels expressing an antifungal protein.  Using a GFP-expressing A. flavus strain we monitored the infection and spread of the fungus in mature kernels in real time. The assay is rapid, reliable, and reproducible.

Video: Inhibition of Aspergillus flavus Growth and Aflatoxin Production in Transgenic Maize Expressing the α-amylase Inhibitor from Lablab purpureus L.

A Rapid and Efficient Method for Assessing Pathogenicity of Ustilago maydis on Maize and Teosinte Lines

Maize is a major cereal crop worldwide. However, susceptibility to biotrophic pathogens is the primary constraint to increasing productivity. U. maydis is a biotrophic fungal pathogen and the causal agent of corn smut on maize. This disease is responsible for significant yield losses of approximately $1.0 billion annually in the U.S.1 Several methods including crop rotation, fungicide application and seed treatments are currently used to control corn smut2. However, host resistance is the only practical method for managing corn smut. Identification of crop plants including maize, wheat, and rice that are resistant to various biotrophic pathogens has significantly decreased yield losses annually3-5. Therefore, the use of a pathogen inoculation method that efficiently and reproducibly delivers the pathogen in between the plant leaves, would facilitate the rapid identification of maize lines that are resistant to U. maydis. As, a first step toward indentifying maize lines that are resistant to U. maydis, a needle injection inoculation method and a resistance reaction screening method was utilized to inoculate maize, teosinte, and maize x teosinte introgression lines with a U. maydis strain and to select resistant plants.
Maize, teosinte and maize x teosinte introgression lines, consisting of about 700 plants, were planted, inoculated with a strain of U. maydis, and screened for resistance. The inoculation and screening methods successfully identified three teosinte lines resistant to U. maydis. Here a detailed needle injection inoculation and resistance reaction screening protocol for maize, teosinte, and maize x teosinte introgression lines is presented. This study demonstrates that needle injection inoculation is an invaluable tool in agriculture that can efficiently deliver U. maydis in between the plant leaves and has provided plant lines that are resistant to U. maydis that can now be combined and tested in breeding programs for improved disease resistance.

A Rapid and Efficient Method for Assessing Pathogenicity of Ustilago maydis on Maize and Teosinte Lines

The use of a needle injection method to inoculate maize and teosinte plants with the biotrophic pathogen Ustilago maydis is described. The needle injection inoculation method facilitates the controlled delivery of the fungal pathogen in between the plant leaves where the pathogen enters the plant through the formation of appresoria. This method is highly efficient, enabling reproducible inoculations with U. maydis.

Maize is a major cereal crop worldwide. However, susceptibility to biotrophic pathogens is the primary constraint to increasing productivity. U. maydis is ...

RNAi-mediated Control of Aflatoxins in Peanut: Method to Analyze Mycotoxin Production and Transgene Expression in the Peanut/Aspergillus Pathosystem

The Food and Agriculture Organization of the United Nations estimates that 25% of the food crops in the world are contaminated with aflatoxins. That represents 100 million tons of food being destroyed or diverted to non-human consumption each year. Aflatoxins are powerful carcinogens normally accumulated by the fungi Aspergillus flavus and A. parasiticus in cereals, nuts, root crops and other agricultural products. Silencing of five aflatoxin-synthesis genes by RNA interference (RNAi) in peanut plants was used to control aflatoxin accumulation following inoculation with A. flavus. Previously, no method existed to analyze the effectiveness of RNAi in individual peanut transgenic events, as these usually produce few seeds, and traditional methods of large field experiments under aflatoxin-conducive conditions were not an option. In the field, the probability of finding naturally contaminated seeds is often 1/100 to 1/1,000. In addition, aflatoxin contamination is not uniformly distributed. Our method uses few seeds per transgenic event, with small pieces processed for real-time PCR (RT-PCR) or small RNA sequencing, and for analysis of aflatoxin accumulation by ultra-performance liquid chromatography (UPLC). RNAi-expressing peanut lines 288-72 and 288-74, showed up to 100% reduction (p&#8804;0.01) in aflatoxin B1 and B2 compared to the control that accumulated up to 14,000 ng.g-1 of aflatoxin B1 when inoculated with aflatoxigenic A. flavus. As reference, the maximum total of aflatoxins allowable for human consumption in the United States is 20 ng.g-1. This protocol describes the application of RNAi-mediated control of aflatoxins in transgenic peanut seeds and methods for its evaluation. We believe that its application in breeding of peanut and other crops will bring rapid advancement in this important area of science, medicine and human nutrition, and will significantly contribute to the international effort to control aflatoxins, and potentially other mycotoxins in major food crops.

RNAi-mediated Control of Aflatoxins in Peanut: Method to Analyze Mycotoxin Production and Transgene Expression in the Peanut/Aspergillus Pathosystem

We demonstrate a method for the analysis of aflatoxins and transgene expression in peanut seeds that contain RNA-interference signals for silencing aflatoxin-synthesis genes in the fungus Aspergillus flavus. RNAi-mediated control of mycotoxins in plants has not been reported previously.

The Food and Agriculture Organization of the United Nations estimates that 25% of the food crops in the world are contaminated with aflatoxins. That ...

Measuring Gene Expression in Bombarded Barley Aleurone Layers with Increased Throughput

The aleurone layer of barley grains is an important model system for hormone-regulated gene expression in plants. In aleurone cells, genes required for germination or early seedling development are activated by gibberellin (GA), while genes associated with stress responses are activated by abscisic acid (ABA). The mechanisms of GA and ABA signaling can be interrogated by introducing reporter gene constructs into aleurone cells via particle bombardment, with the resulting transient expression measured using enzyme assays. An improved protocol is reported that partially automates and streamlines the grain homogenization step and the enzyme assays, allowing significantly more throughput than existing methods. Homogenization of the grain samples is carried out using an automated tissue homogenizer, and GUS (&#946;-glucuronidase) assays are carried out using a 96-well plate system. Representative results using the protocol suggest that phospholipase D activity may play an important role in the activation of HVA1 gene expression by ABA, through the transcription factor TaABF1.

An improved protocol is presented for the measurement of transient gene expression from reporter constructs in barley aleurone cells after particle bombardment. The combination of automated grain grinding with 96-well plate enzyme assays provides high throughput for the procedure.

The aleurone layer of barley grains is an important model system for hormone-regulated gene expression in plants. In aleurone cells, genes required for ...

Genetics

Quantification of Fungal Colonization, Sporogenesis, and Production of Mycotoxins Using Kernel Bioassays

The rotting of grains by seed-infecting fungi poses one of the greatest economic challenges to cereal production worldwide, not to mention serious risks to human and animal health. Among cereal production, maize is arguably the most affected crop, due to pathogen-induced losses in grain integrity and mycotoxin seed contamination. The two most prevalent and problematic mycotoxins for maize growers and food and feed processors are aflatoxin and fumonisin, produced by Aspergillus flavus and Fusarium verticillioides, respectively.
Recent studies in molecular plant-pathogen interactions have demonstrated promise in understanding specific mechanisms associated with plant responses to fungal infection and mycotoxin contamination1,2,3,4,5,6. Because many labs are using kernel assays to study plant-pathogen interactions, there is a need for a standardized method for quantifying different biological parameters, so results from different laboratories can be cross-interpreted. For a robust and reproducible means for quantitative analyses on seeds, we have developed in-lab kernel assays and subsequent methods to quantify fungal growth, biomass, and mycotoxin contamination. Four sterilized maize kernels are inoculated in glass vials with a fungal suspension (106) and incubated for a predetermined period. Sample vials are then selected for enumeration of conidia by hemocytometer, ergosterol-based biomass analysis by high performance liquid chromatography (HPLC), aflatoxin quantification using an AflaTest fluorometer method, and fumonisin quantification by HPLC.

The devastation of cereal crops by seed-infecting fungi has prompted numerous research efforts to better understand plant-pathogen interactions. To study seed-fungal interactions in a laboratory setting, we developed a robust method for the quantification of fungal reproduction, biomass, and mycotoxin contamination using kernel bioassays.

The rotting of grains by seed-infecting fungi poses one of the greatest economic challenges to cereal production worldwide, not to mention serious risks ...

Immunology and Infection

Using Ustilago maydis as a Trojan Horse for In Situ Delivery of Maize Proteins

Inspired by Homer&#180;s Trojan horse myth, we engineered the maize pathogen Ustilago maydis to deliver secreted proteins into the maize apoplast permitting in vivo phenotypic analysis. This method does not rely on maize transformation but exploits microbial genetics and secretory capabilities of pathogens. Herein, it allows inspection of in vivo delivered secreted proteins with high spatiotemporal resolution at different kinds of infection sites and tissues. The Trojan horse strategy can be utilized to transiently complement maize loss-of-function phenotypes, to functionally characterize protein domains, to analyze off-target protein effects, or to study onside protein overdosage, making it a powerful tool for protein studies in the maize crop system. This work contains a precise protocol on how to generate a Trojan horse strain followed by standardized infection protocols to apply this method to three different maize tissue types.

Using Ustilago maydis as a Trojan Horse for In Situ Delivery of Maize Proteins

This work describes the cloning of an Ustilago maydis Trojan horse strain for the in situ delivery of secreted maize proteins into three different types of maize tissues.

Inspired by Homer&#180;s Trojan horse myth, we engineered the maize pathogen Ustilago maydis to deliver secreted proteins into the maize apoplast ...

Lignin Down-regulation of Zea mays via dsRNAi and Klason Lignin Analysis

To facilitate the use of lignocellulosic biomass as an alternative bioenergy resource, during biological conversion processes, a pretreatment step is needed to open up the structure of the plant cell wall, increasing the accessibility of the cell wall carbohydrates. Lignin, a polyphenolic material present in many cell wall types, is known to be a significant hindrance to enzyme access. Reduction in lignin content to a level that does not interfere with the structural integrity and defense system of the plant might be a valuable step to reduce the costs of bioethanol production. In this study, we have genetically down-regulated one of the lignin biosynthesis-related genes, cinnamoyl-CoA reductase (ZmCCR1) via a double stranded RNA interference technique. The ZmCCR1_RNAi construct was integrated into the maize genome using the particle bombardment method. Transgenic maize plants grew normally as compared to the wild-type control plants without interfering with biomass growth or defense mechanisms, with the exception of displaying of brown-coloration in transgenic plants leaf mid-ribs, husks, and stems. The microscopic analyses, in conjunction with the histological assay, revealed that the leaf sclerenchyma fibers were thinned but the structure and size of other major vascular system components was not altered. The lignin content in the transgenic maize was reduced by 7-8.7%, the crystalline cellulose content was increased in response to lignin reduction, and hemicelluloses remained unchanged. The analyses may indicate that carbon flow might have been shifted from lignin biosynthesis to cellulose biosynthesis. This article delineates the procedures used to down-regulate the lignin content in maize via RNAi technology, and the cell wall compositional analyses used to verify the effect of the modifications on the cell wall structure.

Lignin Down-regulation of Zea mays via dsRNAi and Klason Lignin Analysis

A double stranded RNA interference (dsRNAi) technique is employed to down-regulate the maize cinnamoyl coenzyme A reductase (ZmCCR1) gene to lower plant lignin content. Lignin down-regulation from the cell wall is visualized by microscopic analyses and quantified by the Klason method. Compositional changes in hemicellulose and crystalline cellulose are analyzed.

To facilitate the use of lignocellulosic biomass as an alternative bioenergy resource, during biological conversion processes, a pretreatment step is ...

Bioengineering

Direct Liquid-Culture Screening for Evaluating the Production of Heterologous Proteins Using an Auxotrophic Mutant of Aspergillus Oryzae

Aspergillus oryzae, a filamentous fungus, is one of the most widely used hosts for industrial applications including large-scale production of proteins. A polyethylene glycol (PEG)-mediated protoplast transformation method is generally used for the introduction of heterologous genes into A. oryzae. The conventional method typically requires three weeks for the screening of favorable transformants. Here, a new technique, the direct liquid-culture (DLC) screening method, is introduced which reduces the screening time to six days in a 200 mL flask format or to 10 days in a 24 well microplate format. The DLC screening method ensures the acquisition of positive transformants and evaluation of the secretory production of heterologous proteins in a single step, unlike the conventional screening method where two separate steps are required for the same. The protocol for PEG-mediated protoplast transformation of A. oryzae is described, which consists of five steps: preparation of fresh spore suspension, preculture, preparation of protoplasts, introduction of DNA, and DLC screening. For successful results in DLC screening, it is critical to use a nutrient-rich medium with optimized osmotic pressure. The protocol should further popularize the use of A. oryzae as a host of choice in the industrial production of proteins.

Direct Liquid-Culture Screening for Evaluating the Production of Heterologous Proteins Using an Auxotrophic Mutant of Aspergillus Oryzae

A direct liquid-culture (DLC) screening method has been developed which significantly reduces the time required for polyethylene glycol (PEG)-mediated protoplast transformation of the filamentous fungus, Aspergillus oryzae, when employed for evaluation of the secretory production of heterologous proteins. This method dramatically increases the throughput of the evaluation protocol.

Aspergillus oryzae, a filamentous fungus, is one of the most widely used hosts for industrial applications including large-scale production of proteins. A ...

Evaluation of Wild Peanut Species for Resistance to Aflatoxin Accumulation

Non-destructive SPE-UPLC-based Quantification of Aflatoxins and Stilbenoid Phytoalexins in Single Peanut (Arachis spp.) Seeds

Aflatoxins are highly carcinogenic secondary metabolites of some fungal species, particularly Aspergillus flavus. Aflatoxins often contaminate economically important agricultural commodities, including peanuts, posing a high risk to human and animal health. Due to the narrow genetic base, peanut cultivars demonstrate limited resistance to fungal pathogens. Therefore, numerous wild peanut species with tolerance to Aspergillus have received substantial consideration by scientists as sources of disease resistance.
Exploring plant germplasm for resistance to aflatoxins is difficult since aflatoxin accumulation does not follow a normal distribution, which dictates the need for the analyses of thousands of single peanut seeds. Sufficiently hydrated peanut (Arachis spp.) seeds, when infected by Aspergillus species, are capable of producing biologically active stilbenes&#160;(stilbenoids) that are considered defensive phytoalexins. Peanut stilbenes inhibit fungal development and aflatoxin production. Therefore, it is crucial to analyze the same seeds for peanut stilbenoids to explain the nature of seed resistance/susceptibility to the Aspergillus invasion. None of the published methods offer single-seed analyses for aflatoxins and/or stilbene phytoalexins.
We attempted to fulfill the demand for such a method that is environment-friendly, uses inexpensive consumables, and is sensitive and selective. In addition, the method is non-destructive since it uses only half of the seed and leaves the other half containing the embryonic axis intact. Such a technique allows germination and growth of the peanut plant to full maturity from the same seed used for the aflatoxin and stilbenoid analysis. The integrated part of this method, the manual challenging of the seeds with Aspergillus, is a limiting step that requires more time and labor compared to other steps in the method. The method has been used for the exploration of wild Arachis germplasm to identify species resistant to Aspergillus and to determine and characterize novel sources of genetic resistance to this fungal pathogen.

Author Spotlight: Quantification of Aflatoxins and Phytoalexins in Peanut Seeds to Identify Genetic Resistance Against Aspergillus

We demonstrate a medium-throughput method for quantification of aflatoxins and stilbenoid phytoalexins in single peanut seeds using ultra performance liquid chromatography. This method was specifically developed for the analyses of wild Arachis species challenged by the aflatoxigenic Aspergillus species.

Aflatoxins are highly carcinogenic secondary metabolites of some fungal species, particularly Aspergillus flavus. Aflatoxins often contaminate ...

Biochemistry

Agrobacterium-Mediated Immature Embryo Transformation of Recalcitrant Maize Inbred Lines Using Morphogenic Genes

Demonstrated here is a detailed protocol for Agrobacterium-mediated genetic transformation of maize inbred lines using morphogenic genes Baby boom (Bbm) and Wuschel2 (Wus2). Bbm is regulated by the maize phospholipid transferase gene (Pltp) promoter, and Wus2 is under the control of a maize auxin-inducible (Axig1) promoter. An Agrobacterium strain carrying these morphogenic genes on transfer DNA (T-DNA) and extra copies of Agrobacterium virulence (vir) genes are used to infect maize immature embryo explants. Somatic embryos form on the scutella of infected embryos and can be selected by herbicide resistance and germinated into plants. A heat-activated cre/loxP recombination system built into the DNA construct allows for removal of morphogenic genes from the maize genome during an early stage of the transformation process. Transformation frequencies of approximately 14%, 4%, and 4% (numbers of independent transgenic events per 100 infected embryos) can be achieved for W22, B73, and Mo17, respectively, using this protocol.

Agrobacterium-Mediated Immature Embryo Transformation of Recalcitrant Maize Inbred Lines Using Morphogenic Genes

Plant morphogenic genes can be used to improve genetic transformation of recalcitrant genotypes. Described here is an Agrobacterium-mediated genetic transformation (QuickCorn) protocol for three important public maize inbred lines.

Demonstrated here is a detailed protocol for Agrobacterium-mediated genetic transformation of maize inbred lines using morphogenic genes Baby boom (Bbm) ...

Biology

Direct Agroinoculation of Maize Seedlings by Injection with Recombinant Foxtail Mosaic Virus and Sugarcane Mosaic Virus Infectious Clones

Agrobacterium-based inoculation approaches are widely used for introducing viral vectors into plant tissues. This study details a protocol for the injection of maize seedlings near meristematic tissue with Agrobacterium carrying a viral vector. Recombinant foxtail mosaic virus (FoMV) clones engineered for gene silencing and gene expression were used to optimize this method, and its use was expanded to include a recombinant sugarcane mosaic virus (SCMV) engineered for gene expression. Gene fragments or coding sequences of interest are inserted into a modified, infectious viral genome that has been cloned into the binary T-DNA plasmid vector pCAMBIA1380. The resulting plasmid constructs are transformed into Agrobacterium tumefaciens strain GV3101. Maize seedlings as young as 4 days old can be injected near the coleoptilar node with bacteria resuspended in MgSO4 solution. During infection with Agrobacterium, the T-DNA carrying the viral genome is transferred to maize cells, allowing for the transcription of the viral RNA genome. As the recombinant virus replicates and systemically spreads throughout the plant, viral symptoms and phenotypic changes resulting from the silencing of the target genes lesion mimic 22 (les22)&#160;or&#160;phytoene desaturase (pds) can be observed on the leaves, or expression of green fluorescent protein (GFP) can be detected upon illumination with UV light or fluorescence microscopy. To detect the virus and assess the integrity of the insert simultaneously, RNA is extracted from the leaves of the injected plant and RT-PCR is conducted using primers flanking the multiple cloning site (MCS) carrying the inserted sequence. This protocol has been used effectively in several maize genotypes and can readily be expanded to other viral vectors, thereby offering an accessible tool for viral vector introduction in maize.

An Agrobacterium-based injection (agroinjection) protocol is presented for the inoculation of foxtail mosaic virus&#160;and sugarcane mosaic virusclones into maize seedlings. Inoculation in this manner leads to viral infection, virus-induced gene silencing of marker genes, and viral overexpression of GFP.

Inhibition of Aspergillus flavus Growth and Aflatoxin Production in Transgenic Maize Expressing the α-amylase Inhibitor from Lablab purpureus L.

Summary

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Chapters in this video

A Rapid and Efficient Method for Assessing Pathogenicity of Ustilago maydis on Maize and Teosinte Lines

RNAi-mediated Control of Aflatoxins in Peanut: Method to Analyze Mycotoxin Production and Transgene Expression in the Peanut/Aspergillus Pathosystem

Measuring Gene Expression in Bombarded Barley Aleurone Layers with Increased Throughput

Quantification of Fungal Colonization, Sporogenesis, and Production of Mycotoxins Using Kernel Bioassays

Using Ustilago maydis as a Trojan Horse for In Situ Delivery of Maize Proteins

Lignin Down-regulation of Zea mays via dsRNAi and Klason Lignin Analysis

Direct Liquid-Culture Screening for Evaluating the Production of Heterologous Proteins Using an Auxotrophic Mutant of Aspergillus Oryzae

Non-destructive SPE-UPLC-based Quantification of Aflatoxins and Stilbenoid Phytoalexins in Single Peanut (Arachis spp.) Seeds

Agrobacterium-Mediated Immature Embryo Transformation of Recalcitrant Maize Inbred Lines Using Morphogenic Genes

Direct Agroinoculation of Maize Seedlings by Injection with Recombinant Foxtail Mosaic Virus and Sugarcane Mosaic Virus Infectious Clones