Name: inhibition of aspergillus flavus growth and aflatoxin production in transgenic maize expressing the &#945;-amylase inhibitor from lablab purpureus l.
Uploaded: 2019-02-15T15:00:00
Description: Watch this Scientific Journal Video about Inhibition of Aspergillus flavus Growth and Aflatoxin Production in Transgenic Maize Expressing the ÃŽÂ±-amylase Inhibitor from Lablab purpureus L. at JoVE.co

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
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	<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...

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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&#160;Falcon Tissue Culture Dishes, 60 mm</td>
			<td>Fisher Scientific</td>
			<td>08-772F</td>
			<td></td>
		</tr>
		<tr>
			<td>Eppendorf&#160;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>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&#39;&#39;</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&#39;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 ÃŽÂ±-amylase Inhibitor from Lablab purpureus L. at JoVE.co

Inhibition of Aspergillus flavus Growth and Aflatoxin Production in Transgenic Maize Expressing the ÃƒÅ½Ã‚Â±-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 ...

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