The authors would like to thank Jen Sheen of Massachusetts General Hospital for the generous donation of Nicotiana benthamiana seedlings. Jen Bush helped us greatly in advice in growing plants and setting up a growth chamber area. Tom Ferrante of the Wyss Institute offered crucial help with confocal microscopy. The authors would especially like to thank Don Ingber of Children&#8217;s Hospital Boston and the Wyss Institute for the generous donation of a Gene Gun and associated supplies. Funding for this project was provided through a cooperative agreement with the Department of Energy Advanced Research Projects Agency (ARPA- E Award # DE-000079) for PAS, JCW, and MdM, and through Chimerion Biotechnology, Inc. for MJV.

1. Design of Alternatively-spliced Sequences for Multiple Organelle Targeting
<ol>
	<li>Determine the sites for final protein expression. For this work, the interest is in targeting the chloroplast, peroxisome, and cytosol.</li>
	<li>Use the literature to identify protein and DNA sequences known to target proteins to organelles of interest. In this case a chloroplast targeting sequence from Arabidopsis thaliana L-isoaspartate methyltransferase6,15, and a peroxisome targeting sequence from Arabidopsis thaliana transthyretin-like S-allantoin synthase16,17 were determined.</li>
	<li>Identify an alternative-splicing regime that should target the proteins of interest to the correct organelles. For this work, splice sites as observed in a natural Arabidopsis system6. The mRNA sequence was redesigned leaving the natural splice sites, but sequences were placed encoding chloroplast- or peroxisome- targeting tags within the alternatively-spliced introns (Figure 1).</li>
</ol>
2.&#160;Gibson Assembly of DNA Parts
See also Figure 2.
The Gibson assembly method depends on the action of several enzymes in a pre-made mix to 1) partially digest the ends of the double stranded DNA&#8217;s to make single strands and 2) anneal complimentary base pairs of neighboring DNA parts. This allows for cloning of DNA fragments without the limitations of restriction sites.
<ol>
	<li>Choose an order for the elements in the DNA plasmid construct. As an example TriTag-1 has elements of: a) a plasmid vector (pORE, containing a GFP construct known to work in plants, a kanamycin resistance marker, and origins of replication for E. coli and Agrobacterium tumefaciens hosts), b) a promoter sequence, (PENTCUP2, shown to be constitutive in plants), c) a chloroplast targeting sequence (CTS), c) a peroxisome targeting sequence (PTS), and d) a series of splice sites as described previously6.</li>
	<li>Design the construct base-for-base with in silico design software. ApE is an open source freeware package useful for this work. 
	Note: TriTag-1, has the order: plasmid vector, promoter, ATG, splice donor site, chloroplast target sequence, splice donor site, neutral site, splice acceptor site, peroxisome target sequence, splice acceptor site, GFP as contained in plasmid vector.
	<ol>
		<li>Design the in silico DNA construct such that there is a 50-bp overlap between each piece when ordering primers for PCR. It is possible to use the 50 bp overlap as the primers: 25 bp each direction.
		<ol>
			<li>Be sure to keep track of the origin of each of the sequence pieces. Is it as: a plasmid to be grown and miniprepped; a linear sequence that can be used as a PCR template; or a sequence that will need to be synthesized commercially? Several companies offer low-cost DNA synthesis services for fragments &#60;500 bp. In this case, the TriTag itself is 437 bp so it was advantageous to order it commercially.</li>
			<li>The best results will come if all the fragments are PCR-amplified and purified from their template DNA. The resistance marker is a good spot to divide this large DNA into two smaller templates that are more easily PCR-amplified.</li>
			<li>Restriction Restriction enzyme DpnI cuts methylated DNA.&#160; If the PCR template was a miniprep from E. coli, DpnI treatment will remove the contaminating template DNA.</li>
		</ol>
		</li>
	</ol>
	</li>
	<li>Purify all the DNA sequences separately and elute in water, TE or Buffer EB.
	<ol>
		<li>pORE vector part 1, ~3,000 bp (green arrows). PCR amplified and DpnI treated.</li>
		<li>pORE vector part 2, ~3,000 bp (black arrows). PCR amplified and DpnI treated.</li>
		<li>TriTag insert, 437 bp (blue arrows). Ordered commercially. Resuspend in ddH2O.</li>
		<li>PENTCUP promoter, ~750 bp (orange arrows). PCR-amplified and DpnI treated.</li>
	</ol>
	</li>
	<li>Measure the concentrations of each of the DNA pieces. Aim for 150 ng/&#956;l of the vector pieces.</li>
	<li>Take an aliquot of the Gibson assembly mix out of the freezer and thaw on ice. This is commercially available, but also simple to make in lab12&#8211;14.
	<ol>
		<li>There are two steps to this recipe: a viscous 5x master mix and 15 &#956;l reaction-size 1.33x aliquots. The 5x master mix contains: 3 ml 1 M Tris-HCl pH 7.5, 300 &#956;l 1 M MgCl2, 600 &#956;l 10 mM of each dNTP, 300 &#956;l 1 M DTT, 1.5 g PEG-8000, 20 mg NAD, and ddH2O to 6 ml. Prepare 320 &#956;l aliquots (18) and freeze all but one at -20 &#176;C. The solution will be quite viscous. Label these &#8220;5X isotherm buffer&#8221;</li>
		<li>To the one remaining (320 &#956;l), add 1.2 &#956;l T5 Exonuclease, 20 &#956;l Phusion High-Fidelity DNA Polymerase, 160 &#956;l Taq DNA Ligase and 700 &#956;l ddH2O. Prepare 15 &#956;l aliquots (~80) on ice in PCR tubes and store at -20 &#176;C.</li>
	</ol>
	</li>
	<li>Determine volumes for equimolar amounts of each of the fragments. There are a few online calculators, including Gibthon.org. There should be a total of 5 &#956;l of all the DNA pieces. Add them to the 15 &#956;l Gibson mix aliquot. If this requires volumes too small to pipette, dilute the DNA fragments and/or use more than one aliquot.
	<ol>
		<li>Do not forget to prepare a control of the vector DNA alone (e.g. the DNA part containing the antibiotic resistance marker) and make up the volume with water.</li>
	</ol>
	</li>
	<li>Incubate the tubes in a thermal cycler at 50-55 &#176;C for 30-60 minutes. Replace on ice and transform into E. coli via heat-shock chemically competent cells. Do not use electrocompetent cells. The high salt concentration and the relatively low DNA concentration may cause the cells to arc.
	<ol>
		<li>Apply all 20 &#956;l to a commercial preparation of 200 &#956;l calcium-chloride competent E. coli. 
		Incubate on ice 30 min and heat shock 60 sec at 42 &#176;C</li>
		<li>Return to ice 2 min, apply 750 &#956;l SOC or LB medium and recover shaking in a microcentrifuge tube 30 min at 37 &#176;C. Plate the mixture and appropriate dilutions on LB+Kan (or other appropriate antibiotic). This may result in higher background (and a higher number of non-target recombination events) than traditional ligation-based cloning but it is worthwhile to screen about 10 colonies.</li>
	</ol>
	</li>
	<li>Confirm clone via sequence and store an aliquot at -80 &#176;C</li>
</ol>
3.&#160;Biolistic Transfection of Tobacco with the Gene Gun
This is a technique that is established in JoVE18,19. Key steps and differences are described below.
<ol>
	<li>Grow 50-100 ml E. coli or 200 ml Agrobacterium. Maxi-prep the culture. A concentration of about 1,500 ng/&#956;l is required to continue.</li>
	<li>Prepare gene gun bullets as previously described. Load them into the Gene Gun.</li>
	<li>For transfection of Nicotiana benthamiana tobacco leaf epidermal tissue, choose a large leaf close to the base of a 3 month old plant. Carefully cut it and place it bottom side up on wet paper towels in a 15 cm Petri dish.</li>
	<li>Set the He pressure for the Gene Gun to 200-250 psi.</li>
	<li>Carefully aim the Gene Gun between ribs on the bottom side of a leaf, about 3-5 cm above it. Release the safety and deliver the particles to the leaf. Each bullet may be used twice in the same location on the leaf. If the leaf explodes, discard and start a new leaf&#8212;there is some variance in leaf toughness due to growth conditions such as age, moisture, etc. For a 12-cm leaf, expect to fit about 6 shots.</li>
	<li>Store the leaf, covered with the top of a Petri dish for 2-3 days in low light on the bench.</li>
	<li>Examine the leaf in a dissecting microscope equipped with UV fluorescence, and search for individual cells expressing GFP. Dissect 5-10 mm sections of leaf.</li>
	<li>Submerge the leaf in a deep well microscope slide under ~200 &#956;l 0.1% Triton X-100. The detergent helps prevent air bubbles from forming on the surface, and the deep well microscope slide allows for a larger tissue imaging area.</li>
</ol>
4. Confocal Microscopy of Transfected Tissue
These instructions vary for every instrument, so it is essential to get properly trained.
<ol>
	<li>For fluorescence detection experiments, set the excitation laser to 489 nm, and set the photomultiplier detectors to 500-569 nm for GFP fluorescence and 630-700 nm for chlorophyll auto-fluorescence. Image cells using a 40x water-immersion objective.</li>
</ol>

<ol>
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F., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Transgene+regulation+in+plants+by+alternative+splicing+of+a+suicide+exon.">Transgene regulation in plants by alternative splicing of a suicide exon.</a> Nucleic Acids Research. 40 (10), 4701-4710 (2012).</li><li>Syed, N. H., Kalyna, M., Marquez, Y., Barta, A., Brown, J. W. S. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Alternative+splicing+in+plants+-+coming+of+age.">Alternative splicing in plants - coming of age.</a> Trends in Plant Science. 17 (10), 616-623 (2012).</li><li>Black, D. L. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Mechanisms+of+alternative+pre-messenger+RNA+splicing.">Mechanisms of alternative pre-messenger RNA splicing.</a> Annual Review of Biochemistry. 72, 291-336 (2003).</li><li>Dinkins, R. D., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Changing+transcriptional+initiation+sites+and+alternative+5'-+and+3'-splice+site+selection+of+the+first+intron+deploys+Arabidopsis+protein+isoaspartyl+methyltransferase2+variants+to+different+subcellular+compartments.">Changing transcriptional initiation sites and alternative 5'- and 3'-splice site selection of the first intron deploys Arabidopsis protein isoaspartyl methyltransferase2 variants to different subcellular compartments.</a> The Plant Journal: for Cell and Molecular Biology. 55 (1), 1-13 (2008).</li><li>Kebeish, R., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Chloroplastic+photorespiratory+bypass+increases+photosynthesis+and+biomass+production+in+Arabidopsis+thaliana.">Chloroplastic photorespiratory bypass increases photosynthesis and biomass production in Arabidopsis thaliana.</a> Nature Biotechnology. 25 (5), 593-599 (2007).</li><li>Maier, A., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Transgenic+Introduction+of+a+Glycolate+Oxidative+Cycle+into+A.+thaliana+Chloroplasts+Leads+to+Growth+Improvement.">Transgenic Introduction of a Glycolate Oxidative Cycle into A. thaliana Chloroplasts Leads to Growth Improvement.</a> Frontiers in Plant Science. 3 (38), 1-12 (2012).</li><li>Kumar, S., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Remodeling+the+isoprenoid+pathway+in+tobacco+by+expressing+the+cytoplasmic+mevalonate+pathway+in+chloroplasts.">Remodeling the isoprenoid pathway in tobacco by expressing the cytoplasmic mevalonate pathway in chloroplasts.</a> Metabolic Engineering. 14 (1), (2012).</li><li>Sapir-Mir, M., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Peroxisomal+localization+of+Arabidopsis+isopentenyl+diphosphate+isomerases+suggests+that+part+of+the+plant+isoprenoid+mevalonic+acid+pathway+is+compartmentalized+to+peroxisomes.">Peroxisomal localization of Arabidopsis isopentenyl diphosphate isomerases suggests that part of the plant isoprenoid mevalonic acid pathway is compartmentalized to peroxisomes.</a> Plant Physiology. 148 (3), 1219-1228 (2008).</li><li>Voges, M. 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Vis. Exp. (12), (2008).</li><li>Hollender, C. A., Liu, Z. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Bimolecular+Fluorescence+Complementation+(BiFC)+Assay+for+Protein-Protein+Interaction+in+Onion+Cells+Using+the+Helios+Gene.">Bimolecular Fluorescence Complementation (BiFC) Assay for Protein-Protein Interaction in Onion Cells Using the Helios Gene.</a> (40), (2010).</li><li>Li, M. Z., Elledge, S. J. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Harnessing+homologous+recombination+in+vitro+to+generate+recombinant+DNA+via+SLIC.">Harnessing homologous recombination in vitro to generate recombinant DNA via SLIC.</a> Nature Methods. 4 (3), 251-256 (2007).</li></ol>

The authors have nothing to disclose.

In this study, simple strategies are described for localizing a single transgenic protein to multiple cellular compartments in plants. The goal was to design construct that would express a single gene in more than one organelle in Nicotiana benthamiana. Strategies include rational design of GFP-based DNA constructs, Gibson assembly, delivery of the plasmids to leaf cells with the Gene Gun, and observation of the results with confocal microscopy.
Three different short, N-terminal tags ...

This work is a metabolic engineering / synthetic biology project wherein plant cells are engineered to express a reporter protein in multiple organelles but with only a single DNA construct.
One approach to target proteins to more than one location involves cloning multiple genetic copies, each containing a different localization peptide. Each copy must be introduced by successive retransformation, or alternatively, by backcrossing single transforms1. This involves additional cloning, and is limited by one localization tag per terminus.
Another way to localize a protein to multiple locations is through alternative splicing2&#8211;5. RNA is transcribed from a single gene, but different copies of the transcript are processed differently, often in more than one way per cell. This can result in more than one messenger RNA in the cell transcribed from a single gene. These different messenger RNAs can encode for different isoforms of the same protein, or in the case of a frameshift, a different protein altogether. Although alternative splicing has been described in the literature for many years, the mechanisms of action and conserved donor and receptor splice sites are only being elucidated more recently6. As these sites are being better described, they open up opportunities for engineering.
Plant metabolic engineers are faced with a challenge when expressing a protein in multiple organelles. For a protein that is to be localized to more than one organelle, the engineer must clone the same gene multiple times, each with a separate signal sequence directing it to the organelle of interest. For a single gene in three organelles, this is simply three genes. But for a six-gene metabolic pathway, this expands to 18 genes, a significant cloning effort. Combining multiple localization sequences into a single, alternatively-spliced gene significantly reduces this effort. For example, re-engineering photorespiration7,8 and isoprenoid synthesis9,10 involves both the chloroplasts and peroxisomes. In our case we took advantage of splice sites as observed in a natural Arabidopsis thaliana system described previously6. We rationally redesigned the mRNA sequence leaving the natural splice sites alone, but placed sequences that would encode chloroplast- or peroxisome- targeting tags within the alternatively-spliced introns (Figure 1). The expressed protein may or may not have a tag, depending on whether the pre-mRNA that encoded it was excised as an intron (Figures 1g and 1h). For more information on the design of the constructs presented in this work, please see the companion article11.
Because this is still a significant cloning effort, Gibson assembly, a new method for cloning DNA constructs, is used in construction. The Gibson method may be used for any sequence, regardless of restriction sites (Figure 2)12&#8211;14. The specific mix of enzymes allows for a one-step, isothermal assembly. In this method, several double-stranded linear DNA parts are designed such that they have overlapping sequences of ~50 bp. The Gibson assembly enzyme mix partially digests the linear DNA parts, exposing single strands of homologous sequences. These partial single-stranded sequences are re-annealed in the reaction mixture, resulting in a rapid, one-step, sequence-independent, ligation-free subcloning reaction.
This work describes 1) rational design alternatively spliced constructs for expression in plant chloroplasts, peroxisomes, and cytosols, 2) their cloning using the new ligation-free method of Gibson assembly, 3) their delivery into tobacco leaf cells with the Gene Gun, and 4) results showing organelle targeting, as observed with GFP and confocal microscopy.

<table border="0" cellpadding="0" cellspacing="0" width="693">
	<tbody>
		<tr height="21">
			<td height="21" style="height:21px;width:216px;">Oligonucleotide primers</td>
			<td style="width:191px;">IDT</td>
			<td style="width:119px;">(custom)</td>
			<td style="width:167px;">Design specifically for construct</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:216px;">GeneBlocks</td>
			<td style="width:191px;">IDT</td>
			<td style="width:119px;">(custom)</td>
			<td>500 bp oligonucleotides</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:216px;">ApE software</td>
			<td style="width:191px;">U Utah</td>
			<td style="width:119px;">(download)</td>
			<td>http://biologylabs.utah.edu/jorgensen/wayned/ape/</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:216px;">MinElute kit</td>
			<td style="width:191px;">Qiagen</td>
			<td style="width:119px;">28004</td>
			<td>Used to purify PCR products</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:216px;">QIAprep spin miniprep kit</td>
			<td style="width:191px;">Qiagen</td>
			<td style="width:119px;">27104</td>
			<td>Used to prepare cloning-appropriate amounts of plasmid</td>
		</tr>
		<tr height="42">
			<td height="42" style="height:42px;width:216px;">Phusion Master Mix with GC Buffer</td>
			<td style="width:191px;">NEB</td>
			<td style="width:119px;">M0532S</td>
			<td>Used to PCR-amplify gene of interest</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:216px;">Gibson assembly reaction mix</td>
			<td style="width:191px;">NEB</td>
			<td style="width:119px;">E2611L</td>
			<td>Master mix of the following 9 ingredients</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:216px;">1 M Tris-HCl pH7.5</td>
			<td style="width:191px;">Teknova</td>
			<td style="width:119px;">T1075</td>
			<td>Gibson assembly mix</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:216px;">1 M MgCl2</td>
			<td style="width:191px;">G Biosiences</td>
			<td style="width:119px;">82023-086</td>
			<td>Gibson assembly mix</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:216px;">dNTP mix</td>
			<td style="width:191px;">Fermentas</td>
			<td style="width:119px;">R0192</td>
			<td>Gibson assembly mix</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:216px;">1 M DTT</td>
			<td style="width:191px;">Fermentas</td>
			<td style="width:119px;">R0861</td>
			<td>Gibson assembly mix</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:216px;">PEG-8000</td>
			<td style="width:191px;">Affymetrix</td>
			<td style="width:119px;">19966</td>
			<td>Gibson assembly mix</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:216px;">NAD</td>
			<td style="width:191px;">Applichem</td>
			<td style="width:119px;">A1124,0005</td>
			<td>Gibson assembly mix</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:216px;">T5 exonuclease</td>
			<td style="width:191px;">Epicentre</td>
			<td style="width:119px;">T5E4111K</td>
			<td>Gibson assembly mix</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:216px;">Phusion polymerase</td>
			<td style="width:191px;">NEB</td>
			<td style="width:119px;">F530S</td>
			<td>Gibson assembly mix</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:216px;">Taq DNA ligase</td>
			<td style="width:191px;">NEB</td>
			<td style="width:119px;">M0208L</td>
			<td>Gibson assembly mix</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:216px;">Gibthon.org</td>
			<td style="width:191px;"></td>
			<td style="width:119px;"></td>
			<td>Website to simplify calculations</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:216px;">Plasmid PLUS Maxi kit</td>
			<td style="width:191px;">Qiagen</td>
			<td style="width:119px;">12963</td>
			<td>Used to prepare DNA for gene gun bullets</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:216px;">Gene Gun system</td>
			<td style="width:191px;">BioRad</td>
			<td style="width:119px;">165-2451</td>
			<td>Includes all parts necessary</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:216px;">Nicotania benthamiana</td>
			<td style="width:191px;">(n/a)</td>
			<td style="width:119px;">(n/a)</td>
			<td>Gift of Jen Sheen, MGH</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:216px;">Confocal microscope</td>
			<td style="width:191px;">Leica</td>
			<td style="width:119px;">SP5 X MP</td>
			<td>Imaging of resultant cells</td>
		</tr>
		<tr height="42">
			<td height="42" style="height:42px;width:216px;">Deep well slides</td>
			<td style="width:191px;">Electron Microscopy Sciences</td>
			<td style="width:119px;">71561-01</td>
			<td>Used for confocal imaging</td>
		</tr>
		<tr height="42">
			<td height="42" style="height:42px;width:216px;">A Plasmid Editor (ApE) </td>
			<td style="width:191px;">University of Utah </td>
			<td style="width:119px;"></td>
			<td>http://biologylabs.utah.edu/jorgensen/wayned/ape</td>
		</tr>
		<tr height="42">
			<td height="42" style="height:42px;width:216px;">Gibthon:Ligation calculator</td>
			<td style="width:191px;"></td>
			<td style="width:119px;"></td>
			<td>http://django.gibthon.org/tools/ligcalc/</td>
		</tr>
	</tbody>
</table>

transient gene expression in tobacco using gibson assembly and the gene gun

In order to target a single protein to multiple subcellular organelles, plants typically duplicate the relevant genes, and express each gene separately using complex regulatory strategies including differential promoters and/or signal sequences. Metabolic engineers and synthetic biologists interested in targeting enzymes to a particular organelle are faced with a challenge: For a protein that is to be localized to more than one organelle, the engineer must clone the same gene multiple times. This work presents a solution to this strategy: harnessing alternative splicing of mRNA. This technology takes advantage of established chloroplast and peroxisome targeting sequences and combines them into a single mRNA that is alternatively spliced. Some splice variants are sent to the chloroplast, some to the peroxisome, and some to the cytosol. Here the system is designed for multiple-organelle targeting with alternative splicing. In this work, GFP was expected to be expressed in the chloroplast, cytosol, and peroxisome by a series of rationally designed 5&#8217; mRNA tags. These tags have the potential to reduce the amount of cloning required when heterologous genes need to be expressed in multiple subcellular organelles. The constructs were designed in previous work11, and were cloned using Gibson assembly, a ligation independent cloning method that does not require restriction enzymes. The resultant plasmids were introduced into Nicotiana benthamiana epidermal leaf cells with a modified Gene Gun protocol. Finally, transformed leaves were observed with confocal microscopy.

The design effort was a result of significant planning. Novel to this project is the use of alternative splicing to create a pre-mRNA that is translated into differentially expressed proteins. These proteins are expressed in different organelles, in this case the chloroplast, peroxisome and/or cytosol. We adapted natural Arabidopsis gene that is alternatively spliced6, and placed known chloroplast6 and peroxisome17 targeting sequences in alternate exons (TriTag-1 and TriTag-2). T...

Watch this Scientific Journal Video about Transient Gene Expression in Tobacco using Gibson Assembly and the Gene Gun at JoVE.com

Transient Gene Expression in Tobacco using Gibson Assembly and the Gene Gun

This work describes a novel method for selectively targeting subcellular organelles in plants, assayed using the BioRad Gene Gun.

In order to target a single protein to multiple subcellular organelles, plants typically duplicate the relevant genes, and express each gene separately ...

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20.4K Views.  Harvard University. This work describes a novel method for selectively targeting subcellular organelles in plants, assayed using the BioRad Gene Gun.

Video: Transient Gene Expression in Tobacco using Gibson Assembly and the Gene Gun

Determination of Microbial Extracellular Enzyme Activity in Waters, Soils, and Sediments using High Throughput Microplate Assays

Much of the nutrient cycling and carbon processing in natural environments occurs through the activity of extracellular enzymes released by microorganisms. Thus, measurement of the activity of these extracellular enzymes can give insights into the rates of ecosystem level processes, such as organic matter decomposition or nitrogen and phosphorus mineralization. Assays of extracellular enzyme activity in environmental samples typically involve exposing the samples to artificial colorimetric or fluorometric substrates and tracking the rate of substrate hydrolysis. Here we describe microplate based methods for these procedures that allow the analysis of large numbers of samples within a short time frame. Samples are allowed to react with artificial substrates within 96-well microplates or deep well microplate blocks, and enzyme activity is subsequently determined by absorption or fluorescence of the resulting end product using a typical microplate reader or fluorometer. Such high throughput procedures not only facilitate comparisons between spatially separate sites or ecosystems, but also substantially reduce the cost of such assays by reducing overall reagent volumes needed per sample.

Microplate based procedures are described for the colorimetric or fluorometric analysis of extracellular enzyme activity. These procedures allow for the rapid assay of such activity in large numbers of environmental samples within a manageable time frame.

Much of the nutrient cycling and carbon  processing in natural environments occurs through the activity of extracellular  enzymes released by ...

Transcript and Metabolite Profiling for the Evaluation of Tobacco Tree and Poplar as Feedstock for the Bio-based Industry

The global demand for food, feed, energy, and water poses extraordinary challenges for future generations. It is evident that robust platforms for the exploration of renewable resources are necessary to overcome these challenges. Within the multinational framework MultiBioPro we are developing biorefinery pipelines to maximize the use of plant biomass. More specifically, we use poplar and tobacco tree (Nicotiana glauca) as target crop species for improving saccharification, isoprenoid, long chain hydrocarbon contents, fiber quality, and suberin and lignin contents. The methods used to obtain these outputs include GC-MS, LC-MS and RNA sequencing platforms. The metabolite pipelines are well established tools to generate these types of data, but also have the limitations in that only well characterized metabolites can be used. The deep sequencing will allow us to include all transcripts present during the developmental stages of the tobacco tree leaf, but has to be mapped back to the sequence of Nicotiana tabacum. With these set-ups, we aim at a basic understanding for underlying processes and at establishing an industrial framework to exploit the outcomes. In a more long term perspective, we believe that data generated here will provide means for a sustainable biorefinery process using poplar and tobacco tree as raw material. To date the basal level of metabolites in the samples have been analyzed and the protocols utilized are provided in this article.

Plant biomass offers a renewable resource for multiple products, including fuel, feed, food, and a variety of materials. In this paper we investigate the properties of tobacco tree (Nicotiana glauca) and poplar as suitable sources for a biorefinery pipeline.

The global demand for food, feed, energy, and water poses extraordinary challenges for future generations. It is evident that robust platforms for the ...

Tracking Microbial Contamination in Retail Environments Using Fluorescent Powder - A Retail Delicatessen Environment Example

Cross contamination of foodborne pathogens in the retail environment is a significant public health issue contributing to an increased risk for foodborne illness. Ready-to-eat (RTE) processed foods such as deli meats, cheese, and in some cases fresh produce, have been involved in foodborne disease outbreaks due to contamination with pathogens such as Listeria monocytogenes. With respect to L. monocytogenes, deli slicers are often the main source of cross contamination. The goal of this study was to use a fluorescent compound to simulate bacterial contamination and track this contamination in a retail setting. A mock deli kitchen was designed to simulate the retail environment. Deli meat was inoculated with the fluorescent compound and volunteers were recruited to complete a set of tasks similar to those expected of a food retail employee. The volunteers were instructed to slice, package, and store the meat in a deli refrigerator. The potential cross contamination was tracked in the mock retail environment by swabbing specific areas and measuring the optical density of the swabbed area with a spectrophotometer. The results indicated that the refrigerator (i.e. deli case) grip and various areas on the slicer had the highest risk for cross contamination. The results of this study may be used to develop more focused training material for retail employees. In addition, similar methodologies could also be used to track microbial contamination in food production environments (e.g.&#160;small farms), hospitals, nursing homes, cruise ships, and hotels.

The overall goal of this study was to demonstrate the potential cross contamination mechanism of foodborne pathogen Listeria monocytogenes in a retail deli setting. This methodology may be applied to a variety of different environments to track pathogen contamination. &#160;

Cross contamination of foodborne pathogens in the retail environment is a significant public health issue contributing to an increased risk for foodborne ...

Expression of Recombinant Cellulase Cel5A from Trichoderma reesei in Tobacco Plants

Cellulose degrading enzymes, cellulases, are targets of both research and industrial interests. The preponderance of these enzymes in difficult-to-culture organisms, such as hyphae-building fungi and anaerobic bacteria, has hastened the use of recombinant technologies in this field. Plant expression methods are a desirable system for large-scale production of enzymes and other industrially useful proteins. Herein, methods for the transient expression of a fungal endoglucanase, Trichoderma reesei Cel5A, in Nicotiana tabacum are demonstrated. Successful protein expression is shown, monitored by fluorescence using an mCherry-enzyme fusion protein. Additionally, a set of basic tests are used to examine the activity of transiently expressed T. reesei Cel5A, including SDS-PAGE, Western blotting, zymography, as well as&#160;fluorescence and dye-based substrate degradation assays. The system described here can be used to produce an active cellulase in a short time period, so as to assess the potential for further production in plants through constitutive or inducible expression systems.

Expression of Recombinant Cellulase Cel5A from Trichoderma reesei in Tobacco Plants

Tobacco plants were used to produce a fungal cellulase, TrCel5A, via a transient expression system. The expression could be monitored using a fluorescent fusion protein, and the protein activity was characterized post-expression.

Cellulose degrading enzymes, cellulases, are targets of both research and industrial interests. The preponderance of these enzymes in difficult-to-culture ...

Screening Foodstuffs for Class 1 Integrons and Gene Cassettes

Antibiotic resistance is one of the greatest threats to health in the 21st century. Acquisition of resistance genes via lateral gene transfer is a major factor in the spread of diverse resistance mechanisms. Amongst the DNA elements facilitating lateral transfer, the class 1 integrons have largely been responsible for spreading antibiotic resistance determinants amongst Gram negative pathogens. In total, these integrons have acquired and disseminated over 130 different antibiotic resistance genes. With continued antibiotic use, class 1 integrons have become ubiquitous in commensals and pathogens of humans and their domesticated animals. As a consequence, they can now be found in all human waste streams, where they continue to acquire new genes, and have the potential to cycle back into humans via the food chain. This protocol details a streamlined approach for detecting class 1 integrons and their associated resistance gene cassettes in foodstuffs, using culturing and PCR. Using this protocol, researchers should be able to: collect and prepare samples to make enriched cultures and screen for class 1 integrons; isolate single bacterial colonies to identify integron-positive isolates; identify bacterial species that contain class 1 integrons; and characterize these integrons and their associated gene cassettes.

This protocol describes the detection of class 1 integrons and their associated gene cassettes in foodstuffs.

Antibiotic resistance is one of the greatest threats to health in the 21st century. Acquisition of resistance genes via lateral gene transfer is a major ...

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 ...

The Barnacle Balanus improvisus as a Marine Model - Culturing and Gene Expression

Barnacles are marine crustaceans with a sessile adult and free-swimming, planktonic larvae. The barnacle Balanus (Amphibalanus) improvisus is particularly relevant as a model for the studies of osmoregulatory mechanisms because of its extreme tolerance to low salinity. It is also widely used as a model of settling biology, in particular in relation to antifouling research. However, natural seasonal spawning yields an unpredictable supply of cyprid larvae for studies. A protocol for the all-year-round culturing of B. improvisus has been developed and a detailed description of all steps in the production line is outlined (i.e., the establishment of adult cultures on panels, the collection and rearing of barnacle larvae, and the administration of feed for adults and larvae). The description also provides guidance on troubleshooting and discusses critical parameters (e.g., the removal of contamination, the production of high-quality feed, the manpower needed, and the importance of high-quality seawater). Each batch from the culturing system maximally yields roughly 12,000 nauplii and can deliver four batches in a week, so up to almost 50,000 larvae per week can be produced. The method used to culture B. improvisus is, probably, to a large extent also applicable to other marine invertebrates with free-swimminglarvae. Protocols are presented for the dissection of various tissues from adults as well as the production of high-quality RNA for studies on gene expression. It is also described how cultured adults and reared cyprids can be utilized in a wide array of experimental designs for examining gene expression in relation to external factors. The use of cultured barnacles in gene expression is illustrated with studies of possible osmoregulatory roles of Na+/K+ ATPase and aquaporins.

The Barnacle Balanus improvisus as a Marine Model - Culturing and Gene Expression

The barnacle Balanus (Amphibalanus) improvisus is a model for studying osmoregulation and antifouling. However, natural seasonal spawning yields an unpredictable supply of cyprid larvae. Here, a protocol for the all-year-round culturing of B. improvisus is described, including the production of larvae. The use of cultured barnacles in gene expression studies is illustrated.

Barnacles are marine crustaceans with a sessile adult and free-swimming, planktonic larvae. The barnacle Balanus (Amphibalanus) improvisus is particularly ...

Agrobacterium tumefaciens and Agrobacterium rhizogenes-Mediated Transformation of Potato and the Promoter Activity of a Suberin Gene by GUS Staining

Agrobacterium sp. is one of the most widely used methods to obtain transgenic plants as it has the ability to transfer and integrate its own T-DNA into the plant&#39;s genome. Here, we present two transformation systems to genetically modify potato (Solanum tuberosum) plants. In A. tumefaciens transformation, leaves are infected, the transformed cells are selected and a new complete transformed plant is regenerated using phytohormones in 18 weeks. In A. rhizogenes transformation, stems are infected by injecting the bacteria with a needle, the new emerged transformed hairy roots are detected using a red fluorescent marker and the non-transformed roots are removed. In 5-6 weeks, the resulting plant is a composite of a wild type shoot with fully developed transformed hairy roots. To increase the biomass, the transformed hairy roots can be excised and self-propagated. We applied both Agrobacterium-mediated transformation methods to obtain roots expressing the GUS reporter gene driven by a suberin biosynthetic gene promoter. The GUS staining procedure is provided and allows the cell localization of the promoter induction. In both methods, the transformed potato roots showed GUS staining in the suberized endodermis and exodermis, and additionally, in A. rhizogenes transformed roots the GUS activity was also detected in the emergence of lateral roots. These results suggest that A. rhizogenes can be a fast alternative tool to study the genes that are expressed&#160;in roots.

Agrobacterium tumefaciens and Agrobacterium rhizogenes-Mediated Transformation of Potato and the Promoter Activity of a Suberin Gene by GUS Staining

Here, we present two protocols to transform potato plants. The Agrobacterium tumefaciens transformation leads to a complete transgenic plant while the Agrobacterium rhizogenes produces transgenic hairy roots in a wild type shoot that can be self-propagated. We then detect promoter activity by GUS staining in the transformed roots.

Agrobacterium sp. is one of the most widely used methods to obtain transgenic plants as it has the ability to transfer and integrate its own T-DNA into ...

Detached Leaf Assays to Simplify Gene Expression Studies in Potato During Infestation by Chewing Insect Manduca sexta

The multitrophic nature of gene expression studies of insect herbivory demands large numbers of biological replicates, creating the need for simpler, more streamlined herbivory protocols. Perturbations of chewing insects are usually studied in whole plant systems. While this whole organism strategy is popular, it is not necessary if similar observations can be replicated in a single detached leaf. The assumption is that basic elements required for signal transduction are present within the leaf itself. In the case of early events in signal transduction, cells need only to receive the signal from the perturbation and transmit that signal to neighboring cells which are assayed for gene expression.
The proposed method simply changes the timing of the detachment. In whole plant experiments, larvae are confined to a single leaf which is eventually detached from the plant and assayed for gene expression. If the order of excision is reversed, from last in whole plant studies, to first in the detached study, the feeding experiment is simplified.
Solanum tuberosum var. Kennebec is propagated by nodal transfer in a simple tissue culture medium and transferred to soil for further growth if desired. Leaves are excised from the parent plant and relocated to Petri dishes where the feeding assay is conducted with the larval stages of M. sexta. Damaged leaf tissue is assayed for the expression of relatively early events in signal transduction. Gene expression analysis identified infestation-specific Cys2-His2 (C2H2) transcription factors, confirming the success of using detached leaves in early response studies. The method is easier to perform than whole plant infestations and uses less space.

The presented method creates natural herbivore damaged plant tissue through the application of Manduca sexta larvae to detached leaves of potato. The plant tissue is assayed for expression of six transcription factor homologs involved in early responses to insect herbivory.

The multitrophic nature of gene expression studies of insect herbivory demands large numbers of biological replicates, creating the need for simpler, more ...

Leaf Area Index Estimation Using Three Distinct Methods in Pure Deciduous Stands

Accurate estimations of leaf area index (LAI), defined as half of the total leaf surface area per unit of horizontal ground surface area, are crucial for describing the vegetation structure in the fields of ecology, forestry, and agriculture. Therefore, procedures of three commercially used methods (litter traps, needle technique, and a plant canopy analyzer) for performing LAI estimation were presented step-by-step. Specific methodological approaches were compared, and their current advantages, controversies, challenges, and future perspectives were discussed in this protocol. Litter traps are usually deemed as the reference level. Both the needle technique and the plant canopy analyzer (e.g., LAI-2000) frequently underestimate LAI values in comparison with the reference. The needle technique is easy to use in deciduous stands where the litter completely decomposes each year (e.g., oak and beech stands). However, calibration based on litter traps or direct destructive methods is necessary. The plant canopy analyzer is a commonly used device for performing LAI estimation in ecology, forestry, and agriculture, but is subject to potential error due to foliage clumping and the contribution of woody elements in the field of view (FOV) of the sensor. Eliminating these potential error sources was discussed. The plant canopy analyzer is a very suitable device for performing LAI estimations at the high spatial level, observing a seasonal LAI dynamic, and for long-term monitoring of LAI.

An accurate estimation of leaf area index (LAI) is crucial for many models of material and energy fluxes within plant ecosystems and between an ecosystem and the atmospheric boundary layer. Therefore, three methods (litter traps, needle technique, and PCA) for taking precise LAI measurements were in the presented protocol.

Accurate estimations of leaf area index (LAI), defined as half of the total leaf surface area per unit of horizontal ground surface area, are crucial for ...