This work was supported by the Natural Science Foundation of Jiangsu Province (BK20140919), the National Natural Science Foundation of China (31470375), the Priority Academic Program Development of Jiangsu Higher Education Institutions and Qing Lan Project.

1. Preparation of Plants (8 weeks)
<ol>
	<li>Put 50 Nicotiana benthamiana seeds in one 1.5 mL microcentrifuge tube containing 1 mL of 5% NaClO and 0.1% Triton X-100 (V/V) solution and leave for 5 min to sterilize the seeds.</li>
	<li>Rinse the seeds with sterile water 5 times and suspend seeds in 200 &#181;L of sterile water.</li>
	<li>Carefully place individual seeds onto the surface of MS-agar medium (1 L: 1x Murashige &#38; Skoog salts, 10 g sucrose, pH 5.8 (KOH), 1% agar) with fine tips and store medium plates in 4 &#176;C for 3 days to synchronize germination. 
	NOTE: To avoid microbe contamination, perform this step on a clean bench. It is not necessary to shake the tube during sterilization.</li>
	<li>Place medium plates under normal growth conditions (22 &#176;C, 80 - 90 &#181;molm-2s-1 white light intensity) for 10 days, and then transfer the germinated seedlings into soil. 
	NOTE: Make sure to insert seedling roots into soil and do not damage the roots. Cover the tray with a transparent plastic cover overnight to maintain humidity.</li>
	<li>Grow plants in a controlled growth room on a 16 h/8 h light/dark cycle and 70% humidity. 7-week-old N. benthamiana plants are ready for Agrobacteriumtumefaciens infiltration (Figure 1A). 
	NOTE: Water plants and control pests as needed to keep plants healthy.</li>
</ol>
2. Transient Expression in N. Benthamiana Leaves (7 - 10 days)
<ol>
	<li>Deliver 150 ng of plasmids (pEGAD-HA-LUC control plasmid, empty vector, and constructed plasmid for LCI assay, in this case we used pCAMBIA1300-Nluc and pCAMBIA1300-Cluc for plasmid construction) into A. tumefaciens competent cell strain GV3101 with a standard electroporation method.</li>
	<li>Culture A. tumefaciens on Luria-Bertani (LB) agar medium (1 L: 10 g NaCl, 5 g yeast extract, 10 g tryptone, 1.5% agar) containing 50 &#181;g/mL of kanamycin and 50 &#181;g/mL of rifampicin at 28 &#176;C for 4 days. 
	NOTE: The choice of antibiotics depends on the vector and the A. tumefaciens strain used.</li>
	<li>Inoculate one single A. tumefaciens colony from each plate into 3 mL of LB liquid medium containing 50 &#181;g/mL of kanamycin and 50 &#181;g/mL of rifampicin and shake at 220 rpm at 28 &#176;C for 24 h to propagate cell culture.</li>
	<li>Transfer 75 &#181;L of bacterial culture into 15 mL fresh LB liquid medium containing 50 &#181;g/mL of kanamycin and 50 &#181;g/mL of rifampicin, diluting it by a factor of 200. Culture the bacteria at 220 rpm at 30 &#176;C for about 8 h, until OD600 is between 0.5 to 1.0.</li>
	<li>Transfer the A. tumefaciens liquid culture in 15 mL centrifuge tubes and centrifuge at 4,000 x g and 4 &#176;C for 15 min. Discard the supernatant and suspend the pellet in 15 mL of transformation solution to wash pellet.</li>
	<li>Spin the tube at 4,000 x g and 4 &#176;C for 15 min and discard the supernatant. Repeat the washing step once again.</li>
	<li>Resuspend the pellet in 5 mL of transformation solution and keep&#160;for 2 h at room temperature. Adjust the density of A. tumefaciens pellet cells with transformation solution until the final concentration of OD600 is 0.5, or mix two samples with equal volume for testing paired protein interactions.</li>
	<li>Infiltrate suspended cells into the 4th to 7th leaves with a 1 mL needleless syringe (Figure 1B-C). After infiltration, cover plants immediately with a black plastic cover and place the tray in darkness for 12 h. After that, grow plants as usual for 2 to 4 days before detecting LUC activities. 
	NOTE: Choose healthy leaves of similar size. The infiltration of four different zones in one leaf is fine.</li>
</ol>
3. Detecting Luciferase Activity (one day)
Note: There are two ways to monitor luciferase activity. One is based on imaging, and the other is to quantitatively measure luciferase activity.
<ol>
	<li>Imaging method
	<ol>
		<li>Detach an infiltrated leaf and put the entire leaflet on MS-agar medium.</li>
		<li>Spray luciferin working buffer onto the leaf adaxial surface with a 50-mL spray bottle. Keep the materials in the dark for 5 min to quench the chlorophyll auto-fluorescence.</li>
		<li>Use a low-light cooled CCD imaging apparatus (cooled to -30 &#176;C) to capture images (Figure 2). The light-filed exposure time is 50 ms, and luminescence detection time is 1 min. 
		&#8203;NOTE: Adjust the parameters according to the machine manual. Lower temperatures will enhance the signal-noise ratio to improve image quality.</li>
	</ol>
	</li>
	<li>Alternatively, measure luminescence directly with a commercial luminometer.
	<ol>
		<li>Carefully cut out leaf fragments (about 0.25 cm2) from the infiltration area of the N. benthamiana leaves and immerse the leaf disk into 100 &#181;L of deionized water in a 96-well white plate (Figure 3).</li>
		<li>Add 10 &#181;L of luciferin working buffer and leave for 5 min. Then perform specific treatments to study the protein interaction dynamics. 
		NOTE: Detect the luminescence with a luminometer at different time points to obtain the luciferase activity dynamics, which represent the kinetics of protein-protein interactions under certain treatment. This method has advantages for testing a large number of protein pairs simultaneously. For those without a commercial luminometer, examine the luciferase protein abundances by western blot, therefore refer to the LUC activity quantitively. If light is not necessarily required, just keep the plate in the luminometer and measure luminescence at different time points. Otherwise, move the plate into a growth chamber during the detection gap. To obtain statistically significant results, use at least three biological replicates. Although LUC activities from different infiltration zones will vary, their changing patterns are consistent after normalization.</li>
	</ol>
	</li>
</ol>

<ol>
	<li>Thines, B., 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=JAZ+repressor+proteins+are+targets+of+the+SCF(COI1)+complex+during+jasmonate+signalling.">JAZ repressor proteins are targets of the SCF(COI1) complex during jasmonate signalling.</a> Nature. 448, 661-665 (2007).</li><li>Chini, 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=The+JAZ+family+of+repressors+is+the+missing+link+in+jasmonate+signalling.">The JAZ family of repressors is the missing link in jasmonate signalling.</a> Nature. 448, 666-671 (2007).</li><li>Jones, A. 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=Border+control--a+membrane-linked+interactome+of+Arabidopsis.">Border control--a membrane-linked interactome of Arabidopsis.</a> Science. 344, 711-716 (2014).</li><li>Arabidopsis Interactome Mapping Consortium. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Evidence+for+network+evolution+in+an+Arabidopsis+interactome+map.">Evidence for network evolution in an Arabidopsis interactome map.</a> Science. 333, 601-607 (2011).</li><li>Yazaki, J., 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=Mapping+transcription+factor+interactome+networks+using+HaloTag+protein+arrays.">Mapping transcription factor interactome networks using HaloTag protein arrays.</a> Proc Natl Acad Sci U S A. 113, 4238-4247 (2016).</li><li>Kenworthy, A. K. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Imaging+protein-protein+interactions+using+fluorescence+resonance+energy+transfer+microscopy.">Imaging protein-protein interactions using fluorescence resonance energy transfer microscopy.</a> Methods. 24, 289-296 (2001).</li><li>Walter, 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=Visualization+of+protein+interactions+in+living+plant+cells+using+bimolecular+fluorescence+complementation.">Visualization of protein interactions in living plant cells using bimolecular fluorescence complementation.</a> Plant J. 40, 428-438 (2004).</li><li>Chen, H., 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=Firefly+luciferase+complementation+imaging+assay+for+protein-protein+interactions+in+plants.">Firefly luciferase complementation imaging assay for protein-protein interactions in plants.</a> Plant Physiol. 146, 368-376 (2008).</li><li>Layton, C. J., Hellinga, H. W. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Quantitation+of+protein-protein+interactions+by+thermal+stability+shift+analysis.">Quantitation of protein-protein interactions by thermal stability shift analysis.</a> Protein Sci. 20, 1439-1450 (2011).</li><li>Schuck, P. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Reliable+determination+of+binding+affinity+and+kinetics+using+surface+plasmon+resonance+biosensors.">Reliable determination of binding affinity and kinetics using surface plasmon resonance biosensors.</a> Curr Opin Biotechnol. 8, 498-502 (1997).</li><li>Huang, X., Ouyang, X., Deng, X. W. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Beyond+repression+of+photomorphogenesis:+role+switching+of+COP/DET/FUS+in+light+signaling.">Beyond repression of photomorphogenesis: role switching of COP/DET/FUS in light signaling.</a> Current opinion in plant biology. 21, 96-103 (2014).</li><li>Liu, B., Zuo, Z., Liu, H., Liu, X., Lin, C. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Arabidopsis+cryptochrome+1+interacts+with+SPA1+to+suppress+COP1+activity+in+response+to+blue+light.">Arabidopsis cryptochrome 1 interacts with SPA1 to suppress COP1 activity in response to blue light.</a> Genes Dev. 25, 1029-1034 (2011).</li><li>Lian, H. L., 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=Blue-light-dependent+interaction+of+cryptochrome+1+with+SPA1+defines+a+dynamic+signaling+mechanism.">Blue-light-dependent interaction of cryptochrome 1 with SPA1 defines a dynamic signaling mechanism.</a> Genes Dev. 25, 1023-1028 (2011).</li><li>Zuo, Z., Liu, H., Liu, B., Liu, X., Lin, C. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Blue+light-dependent+interaction+of+CRY2+with+SPA1+regulates+COP1+activity+and+floral+initiation+in+Arabidopsis.">Blue light-dependent interaction of CRY2 with SPA1 regulates COP1 activity and floral initiation in Arabidopsis.</a> Curr Biol. 21, 841-847 (2011).</li></ol>

The authors have nothing to disclose.

The protocol described here is simple and reproducible for studying in vivo protein-protein interactions, and particularly suitable for detecting protein interaction dynamics under exogenous treatment. The key step in this assay is N. benthamiana infiltration. To ensure infiltration success, plants must be very healthy. Another critical factor is when to check luciferase activity after infiltration. There is no correct answer for this question. Researchers are encouraged to monitor luciferase activity a...

In order to coordinate growth with its environment, plants have evolved elegant signaling pathways to sense, transduce, and respond to signaling cues. Like the runners in a relay race, proteins are necessary players in plant signal transduction. It has been widely recognized that protein-protein interaction (PPI) plays a major role for cellular communication. Protein phosphorylation, acetylation, and degradation are all dependent on physical interaction between a target protein and its modifying enzymes. For example, Jasmonate ZIM-domain protein (JAZ) family proteins interact with transcription factor MYC2 and suppress its transcriptional activity1,2. Given the importance of PPI, large-scale protein interactomes in plants have been explored recently3,4,5. These interactome results further reveal the complex regulatory network that coordinates diverse cellular functions.
There are some established approaches for monitoring PPI. The yeast two hybrid (Y2H) assay is the most widely used method for PPI detection. Y2H is easy to perform, and suitable for a quick test to examine protein interactions. Y2H is also widely used for screening unknown interaction partners for the specific protein-of-interest. However, because Y2H is entirely carried out in yeast, it cannot reflect the real scenario in plant cells and brings high false positive rates. Another similar strategy is the pull-down assay. In general, two proteins are expressed and purified from Escherichia coli cells and then mixed and immobilized for detecting protein interactions. Although this method is not time-consuming, it cannot obtain in vivo interaction results either. For in vivo interaction purposes, co-immunoprecipitation (co-IP) is the most popular assay, which requires high quality antibody to immunoprecipitate the protein-of-interest and cannot exclude the possibility of indirect PPIs. Moreover, due to the complicated experimental procedures in co-IP, the results usually vary with individual expertise.
Reporter based reconstitution assays greatly advance the detection of in vivo PPI. These methods include fluorescence resonance energy transfer (FRET)6, bimolecular fluorescence complementation (BiFC)7, and the firefly luciferase complementation imaging (LCI) assay8. Although these three approaches are better than co-IP to reflect the direct in vivo PPI, FRET, and BiFC need specific microscopes to detect fluorescence signals and cannot easily quantify the interaction intensity. In contrast, LCI takes advantage of firefly luciferase, which will glow after reacting with its substrate luciferin. More importantly, PPI intensity can be determined from the value of luciferase activity. Thus, LCI not only indicates whether two proteins interact or not, but also provides information on the interaction dynamics upon treatment. Although there are some established methods for monitoring interaction dynamics (based on surface plasmon resonance or thermo-stability shifts)9,10, these approaches require delicate instruments or specific labeling. In contrast, LCI is easier to perform and detect.
The principle for LCI is that the amino-terminal and carboxyl-terminal halves of luciferase (named N-Luc or C-Luc, respectively) were fused with protein A and B, and these two fusion proteins were simultaneously expressed in plant cells. If protein A interacts with protein B, then the two halves of luciferase will be reconstituted to be an active luciferase enzyme. Luciferase activity can be detected with a luminometer or CCD-camera. It is not necessary to obtain stable transformants for LCI; transient expression is enough to get a high-quality interaction result.
RING-type E3 ubiquitin ligase constitutive photomorphogenic 1 (COP1) interacts with a myriad of transcription factors and promotes their degradation through the 26S proteasome11. Some of these COP1-targeted transcription factors are positive regulators for photomorphogenesis. In darkness, COP1 interacts with suppressor of phytochrome A-105 1 (SPA1), which enhances COP1 E3 activity8. After perception of light, photoreceptors will abrogate the COP1-SPA1 interaction to inhibit COP1 activity and then stabilize COP1 substrates12,13,14. This example illustrates the biological significance of studying PPI and determining PPI dynamics.

<table style="border-collapse:collapse;width:686pt" width="915">
	<colgroup>
		<col style="width:293pt" width="390" />
		<col style="width:140pt" width="186" />
		<col style="width:140pt" width="187" />
		<col style="width:114pt" width="152" />
	</colgroup>
	<tbody>
		<tr height="28" style="height:21.0pt">
			<td class="xl16" height="28" style="width:293pt;height:21.0pt" width="390">Transformation solution</td>
			<td class="xl16" style="width:140pt" width="186"></td>
			<td class="xl16" style="width:140pt" width="187"></td>
			<td style="width:114pt" width="152"></td>
		</tr>
		<tr height="28" style="height:21.0pt">
			<td class="xl17" height="28" style="width:293pt;height:21.0pt" width="390">10 mM Morpholineethanesulfonic acid</td>
			<td class="xl17" style="width:140pt" width="186">VETEC</td>
			<td class="xl17" style="width:140pt" width="187">V900336&#160;</td>
			<td></td>
		</tr>
		<tr height="28" style="height:21.0pt">
			<td class="xl17" height="28" style="width:293pt;height:21.0pt" width="390">27.8 mM Glucose</td>
			<td class="xl17" style="width:140pt" width="186">VETEC</td>
			<td class="xl17" style="width:140pt" width="187">V900392</td>
			<td></td>
		</tr>
		<tr height="32" style="height:24.0pt">
			<td class="xl18" height="32" style="width:293pt;height:24.0pt" width="390">10 mM MgCl2&#215;6H2O</td>
			<td class="xl17" style="width:140pt" width="186">VETEC</td>
			<td class="xl17" style="width:140pt" width="187">V900020&#160;</td>
			<td></td>
		</tr>
		<tr height="28" style="height:21.0pt">
			<td class="xl17" height="28" style="width:293pt;height:21.0pt" width="390">150 &#956;M Acetosyringone</td>
			<td class="xl17" style="width:140pt" width="186">ALDRICH</td>
			<td class="xl17" style="width:140pt" width="187">D134406&#160;</td>
			<td></td>
		</tr>
		<tr height="28" style="height:21.0pt">
			<td class="xl17" height="28" style="width:293pt;height:21.0pt" width="390">pH 5.7</td>
			<td class="xl17" style="width:140pt" width="186"></td>
			<td class="xl17" style="width:140pt" width="187"></td>
			<td></td>
		</tr>
		<tr height="28" style="height:21.0pt">
			<td class="xl16" height="28" style="width:293pt;height:21.0pt" width="390">Luciferin working buffer</td>
			<td class="xl17" style="width:140pt" width="186"></td>
			<td class="xl17" style="width:140pt" width="187"></td>
			<td></td>
		</tr>
		<tr height="56" style="height:42.0pt">
			<td class="xl17" height="56" style="width:293pt;height:42.0pt" width="390">5 mM Luciferin potassium salt</td>
			<td class="xl17" style="width:140pt" width="186">GOLD BIOTECHNOLOGY</td>
			<td class="xl17" style="width:140pt" width="187">LUCK-100</td>
			<td></td>
		</tr>
		<tr height="28" style="height:21.0pt">
			<td class="xl17" height="28" style="width:293pt;height:21.0pt" width="390">0.025% Triton X-100</td>
			<td class="xl17" style="width:140pt" width="186">VETEC</td>
			<td class="xl17" style="width:140pt" width="187">V900502&#160;</td>
			<td></td>
		</tr>
		<tr height="32" style="height:24.0pt">
			<td class="xl17" height="32" style="width:293pt;height:24.0pt" width="390">H2O to 10 ml</td>
			<td class="xl21"></td>
			<td class="xl21"></td>
			<td></td>
		</tr>
	</tbody>
</table>

luciferase complementation imaging assay in nicotiana benthamiana leaves for transiently determining protein-protein interaction dynamics

Protein-protein interactions are fundamental mechanisms for relaying signal transduction in most cellular processes; therefore, identification of novel protein-protein interaction pairs and monitoring protein interaction dynamics are of particular interest for revealing how plants respond to environmental factors and/or developmental signals. A plethora of approaches have been developed to examine protein-protein interactions, either in vitro or in vivo. Among them, the recently established luciferase complementation imaging (LCI) assay is the simplest and fastest method for demonstrating in vivo protein-protein interactions. In this assay, protein A or protein B is fused with the amino-terminal or carboxyl-terminal half of luciferase, respectively. When protein A interacts with protein B, the two halves of luciferase will be reconstituted to form a functional and active luciferase enzyme. Luciferase activity can be recorded with a luminometer or CCD-camera. Compared with other approaches, the LCI assay shows protein-protein interactions both qualitatively and quantitatively. Agrobacterium infiltration in Nicotiana benthamiana leaves is a widely used system for transient protein expression. With the combination of LCI and transient expression, these approaches show that the physical interaction between COP1 and SPA1 was gradually reduced after jasmonate treatment.

Three major steps can be singled out in this luciferase complementation protocol for studying protein-protein interactions in vivo, including plant growth, tobacco infiltration, and the luciferase assay. The most crucial step in this protocol is infiltrating liquid A. tumefaciens into N. benthamiana leaves (Figure 1).
Here is an example of the usefulness of this technique ...

Watch this Scientific Journal Video about Luciferase Complementation Imaging Assay in Nicotiana benthamiana Leaves for Transiently Determining Protein-protein Interaction Dynamics at JoVE.com

Luciferase Complementation Imaging Assay in Nicotiana benthamiana Leaves for Transiently Determining Protein-protein Interaction Dynamics

This manuscript describes an easy and rapid experimental procedure for determining protein-protein interactions based on the measurement of luciferase activity.

Luciferase Complementation Imaging Assay in Nicotiana benthamiana Leaves for Transiently Determining Protein-protein Interaction Dynamics

Protein-protein interactions are fundamental mechanisms for relaying signal transduction in most cellular processes; therefore, identification of novel ...

luciferase-complementation-imaging-assay-nicotiana-benthamiana-leaves

Research

JoVE Journal

Biology

13.7K Views.  Nanjing Normal University. This manuscript describes an easy and rapid experimental procedure for determining protein-protein interactions based on the measurement of luciferase activity.

Video: Luciferase Complementation Imaging Assay in Nicotiana benthamiana Leaves for Transiently Determining Protein-protein Interaction Dynamics

Bimolecular Fluorescence Complementation (BiFC) Assay for Protein-Protein Interaction in Onion Cells Using the Helios Gene Gun

Investigation of gene function in diverse organisms relies on knowledge of how the gene products interact with each other in their normal cellular environment. The Bimolecular Fluorescence Complementation (BiFC) Assay1 allows researchers to visualize protein-protein interactions in living cells and has become an essential research tool. This assay is based on the facilitated association of two fragments of a fluorescent protein (GFP) that are each fused to a potential interacting protein partner. The interaction of the two protein partners would facilitate the association of the N-terminal and C-terminal fragment of GFP, leading to fluorescence. For plant researchers, onion epidermal cells are an ideal experimental system for conducting the BiFC assay because of the ease in obtaining and preparing onion tissues and the direct visualization of fluorescence with minimal background fluorescence. The Helios Gene Gun (BioRad) is commonly used for bombarding plasmid DNA into onion cells. We demonstrate the use of Helios Gene Gun to introduce plasmid constructs for two interacting Arabidopsis thaliana transcription factors, SEUSS (SEU) and LEUNIG HOMOLOG (LUH)2 and the visualization of their interactions mediated by BiFC in onion epidermal cells.

Bimolecular Fluorescence Complementation BiFC Assay for Protein-Protein Interaction in Onion Cells Using the Helios Gene Gun

This article illustrates how to properly use the BioRad Helios Gene Gun to introduce plasmid DNA into onion epidermal cells and how to test for protein-protein interactions in onion cells based on the principle of Bimolecular Fluorescence Complementation (BiFC)

Investigation of gene function in diverse organisms relies on knowledge of how the gene products interact with each other in their normal cellular ...

Detection of Protein Interactions in Plant using a Gateway Compatible Bimolecular Fluorescence Complementation (BiFC) System

We have developed a BiFC technique to test the interaction between two proteins in vivo. This is accomplished by splitting a yellow fluorescent protein (YFP) into two non-overlapping fragments. Each fragment is cloned in-frame to a gene of interest. These constructs can then be co-transformed into Nicotiana benthamiana via Agrobacterium mediated transformation, allowing the transit expression of fusion proteins. The reconstitution of YFP signal only occurs when the inquest proteins interact 1-7. To test and validate the protein-protein interactions, BiFC can be used together with yeast two hybrid (Y2H) assay. This may detect indirect interactions which can be overlooked in the Y2H. Gateway technology is a universal platform that enables researchers to shuttle the gene of interest (GOI) into as many expression and functional analysis systems as possible8,9. Both the orientation and reading frame can be maintained without using restriction enzymes or ligation to make expression-ready clones. As a result, one can eliminate all the re-sequencing steps to ensure consistent results throughout the experiments. We have created a series of Gateway compatible BiFC and Y2H vectors which provide researchers with easy-to-use tools to perform both BiFC and Y2H assays10. Here, we demonstrate the ease of using our BiFC system to test protein-protein interactions in N. benthamiana plants.

Detection of Protein Interactions in Plant using a Gateway Compatible Bimolecular Fluorescence Complementation BiFC System

We have developed a technique to test protein-protein interactions in plant. A yellow fluorescent protein (YFP) is split into two non-overlapping fragments. Each fragment is cloned in-frame to a gene of interest via Gateway system, enabling expression of fusion proteins. Reconstitution of YFP signal only occurs when the inquest proteins interact.

We have developed a BiFC technique to test the interaction between two proteins in vivo. This is accomplished by splitting a yellow fluorescent protein ...

TurboID-Based Proximity Labeling for In Planta Identification of Protein-Protein Interaction Networks

Proximity labeling (PL) techniques using engineered ascorbate peroxidase (APEX) or Escherichia coli biotin ligase BirA (known as BioID) have been successfully used for identification of protein-protein interactions (PPIs) in mammalian cells. However, requirements of toxic hydrogen peroxide (H2O2) in APEX-based PL, longer incubation time with biotin (16&#8211;24 h), and higher incubation temperature (37 &#176;C) in BioID-based PL severely limit their applications in plants. The recently described TurboID-based PL addresses many limitations of BioID and APEX. TurboID allows rapid proximity labeling of proteins in just 10&#8201;min under room temperature (RT) conditions. Although the utility of TurboID has been demonstrated in animal models, we recently showed that TurboID-based PL performs better in plants compared to BioID for labeling of proteins that are proximal to a protein of interest. Provided here is a step-by-step protocol for the identification of protein interaction partners using the N-terminal Toll/interleukin-1 receptor (TIR) domain of the nucleotide-binding leucine-rich repeat (NLR) protein family as a model. The method describes vector construction, agroinfiltration of protein expression constructs, biotin treatment, protein extraction and desalting, quantification, and enrichment of the biotinylated proteins by affinity purification. The protocol described here can be easily adapted to study other proteins of interest in Nicotiana and other plant species.

Described here is a proximity labeling method for identification of interaction partners of the TIR domain of the NLR immune receptor in Nicotiana benthamiana leaf tissue. Also provided is a detailed protocol for the identification of interactions between other proteins of interest using this technique in Nicotiana and other plant species.

Proximity labeling (PL) techniques using engineered ascorbate peroxidase (APEX) or Escherichia coli biotin ligase BirA (known as BioID) have been ...

Immunology and Infection

Optimization and Utilization of Agrobacterium-mediated Transient Protein Production in Nicotiana

Agrobacterium-mediated transient protein production in plants is a promising approach to produce vaccine antigens and therapeutic proteins within a short period of time. However, this technology is only just beginning to be applied to large-scale production as many technological obstacles to scale up are now being overcome. Here, we demonstrate a simple and reproducible method for industrial-scale transient protein production based on vacuum infiltration of Nicotiana plants with Agrobacteria carrying launch vectors. Optimization of Agrobacterium cultivation in AB medium allows direct dilution of the bacterial culture in Milli-Q water, simplifying the infiltration process. Among three tested species of Nicotiana, N. excelsiana (N. benthamiana &#215; N. excelsior) was selected as the most promising host due to the ease of infiltration, high level of reporter protein production, and about two-fold higher biomass production under controlled environmental conditions. Induction of Agrobacterium harboring pBID4-GFP (Tobacco mosaic virus-based) using chemicals such as acetosyringone and monosaccharide had no effect on the protein production level. Infiltrating plant under 50 to 100 mbar for 30 or 60 sec resulted in about 95% infiltration of plant leaf tissues. Infiltration with Agrobacterium laboratory strain GV3101 showed the highest protein production compared to Agrobacteria laboratory strains LBA4404 and C58C1 and wild-type Agrobacteria strains at6, at10, at77 and A4. Co-expression of a viral RNA silencing suppressor, p23 or p19, in N. benthamiana resulted in earlier accumulation and increased production (15-25%) of target protein (influenza virus hemagglutinin).

Optimization and Utilization of Agrobacterium-mediated Transient Protein Production in Nicotiana

Transient protein production in Nicotiana plants based on vacuum infiltration with Agrobacteria carrying launch vectors (Tobacco mosaic virus-based) is a rapid and economic approach to produce vaccine antigens and therapeutic proteins. We simplified the procedure and improved target accumulation by optimizing conditions of bacteria cultivation, selecting host species, and co-introducing RNA silencing suppressors.

Agrobacterium-mediated transient protein production in plants is a promising approach to produce vaccine antigens and therapeutic proteins within a short ...

Protein-protein Interactions Visualized by Bimolecular Fluorescence Complementation in Tobacco Protoplasts and Leaves

Many proteins interact transiently with other proteins or are integrated into multi-protein complexes to perform their biological function. Bimolecular fluorescence complementation (BiFC) is an in vivo method to monitor such interactions in plant cells. In the presented protocol the investigated candidate proteins are fused to complementary halves of fluorescent proteins and the respective constructs are introduced into plant cells via agrobacterium-mediated transformation. Subsequently, the proteins are transiently expressed in tobacco leaves and the restored fluorescent signals can be detected with a confocal laser scanning microscope in the intact cells. This allows not only visualization of the interaction itself, but also the subcellular localization of the protein complexes can be determined. For this purpose, marker genes containing a fluorescent tag can be coexpressed along with the BiFC constructs, thus visualizing cellular structures such as the endoplasmic reticulum, mitochondria, the Golgi apparatus or the plasma membrane. The fluorescent signal can be monitored either directly in epidermal leaf cells or in single protoplasts, which can be easily isolated from the transformed tobacco leaves. BiFC is ideally suited to study protein-protein interactions in their natural surroundings within the living cell. However, it has to be considered that the expression has to be driven by strong promoters and that the interaction partners are modified due to fusion of the relatively large fluorescence tags, which might interfere with the interaction mechanism. Nevertheless, BiFC is an excellent complementary approach to other commonly applied methods investigating protein-protein interactions, such as coimmunoprecipitation, in vitro pull-down assays or yeast-two-hybrid experiments.

Formation of protein complexes in vivo can be visualized by bimolecular fluorescence complementation. Interaction partners are fused to complementary parts of fluorescent tags and transiently expressed in tobacco leaves, resulting in a reconstituted fluorescent signal upon close proximity of the two proteins.

Many proteins interact transiently with other proteins or are integrated into multi-protein complexes to perform their biological function. Bimolecular ...

Imaging Spatial Reorganization of a MAPK Signaling Pathway Using the Tobacco Transient Expression System

Visualization of dynamic signaling events in live cells has been a challenge. We expanded an established transient expression system, the biomolecular fluorescent complementation (BiFC) assay in tobacco epidermal cells, from testing protein-protein interaction to monitoring spatial distribution of signal transduction in plant cells. In this protocol, we used the BiFC assay to show that the interaction and the signaling between the Arabidopsis MAPKKK YODA and MAPK6 occur at the plasma membrane. When the scaffold protein BASL was co-expressed, the YODA-MAPK interaction redistributed and spatially co-polarized with CFP-BASL. This modified tobacco expression system allows for quick examination of signaling localization and dynamic changes (less than 4 days) and can accommodate multiple of fluorescent protein colors (at least three). We also presented detailed methods to quantify protein distribution (asymmetric spatial localization, or &#34;polarization&#34;) in tobacco cells. This advanced tobacco expression system has a potential to be used widely for quick testing of dynamic signaling events in live plant cells.

At the subcellular level, signaling events are dynamically modulated by developmental and environmental cues. Here we describe a protocol that employs the tobacco transient expression system to monitor dynamic protein-protein interaction and to disclose spatial organization of signal transduction in plant cells.

Visualization of dynamic signaling events in live cells has been a challenge. We expanded an established transient expression system, the biomolecular ...

Demonstration of Heterologous Complexes formed by Golgi-Resident Type III Membrane Proteins using Split Luciferase Complementation Assay

The goal of this protocol is to explore the applicability of the most recent variant of split luciferase complementation for demonstrating heterologous complexes formed by nucleotide sugar transporters (NSTs). These ER- and Golgi-resident multitransmembrane proteins carry the cytoplasmically synthesized nucleotide sugars across organelle membranes to supply enzymes that mediate glycosylation with their substrates. NSTs exist as dimers and/or higher oligomers. Heterologous interactions between&#160;different NSTs have also been reported. To verify whether the technique is suitable for studying the phenomenon of NST heteromerization, we tested it against a combination of the two Golgi-resident NSTs that have been previously shown to associate by several other means. The&#160;luciferase complementation assay appears to be particularly suitable for studying interactions between Golgi-resident membrane proteins, as it does not require high expression levels, which often trigger protein mislocalization and increase the risk of false positives.

The&#160;protocol presented here is intended to demonstrate the occurrence of heterologous interactions between Golgi-resident type III membrane proteins with cytoplasmically exposed N- and/or C-termini in live mammalian cells using the most recent variant of the split luciferase complementation assay.

The goal of this protocol is to explore the applicability of the most recent variant of split luciferase complementation for demonstrating heterologous ...

Determination of Tripartite Interaction between Two Monomers of a MADS-box Transcription Factor and a Calcium Sensor Protein by BiFC-FRET-FLIM Assay

Protein-protein interactions are an integral part of all biological processes in the cells as they play a crucial role in regulating, maintaining, and amending cellular functions. These interactions are involved in a wide range of phenomena such as signal transduction, pathogen response, cell-cell interactions, metabolic and developmental processes. In the case of transcription factors, these interactions may lead to oligomerization of subunits, sequestering in specific subcellular contexts such as the nucleus, cytoplasm, etc., which, in turn, might have a more profound effect on the expression of the downstream genes. Here, we demonstrate a methodology to visualize in vivo tripartite interaction using Bimolecular Fluorescence Complementation (BiFC) based F&#246;rster Resonance Energy Transfer (FRET) involving Fluorescence Lifetime Imaging (FLIM). Two of the proteins selected for this demonstration interact as BiFC partners, and their reconstituted fluorescence activity is used to assay FRET-FLIM with the third partner. Four to five-week-old growth-chamber-grown Nicotiana benthamiana plants have been used as the model plant system for this demonstration.

Here we present, a method to visualize ternary complex formation between three protein partners using fluorescent-tagged proteins by BiFC based FRET-FLIM assay. This method is valuable for studying protein-protein interaction complexes in vivo.

Protein-protein interactions are an integral part of all biological processes in the cells as they play a crucial role in regulating, maintaining, and ...

Investigating Interactions Between Histone Modifying Enzymes and Transcription Factors in vivo by Fluorescence Resonance Energy Transfer

Epigenetic regulation of gene expression is commonly affected by histone modifying enzymes (HMEs) that generate heterochromatic or euchromatic histone marks for transcriptional repression or activation, respectively. HMEs are recruited to their target chromatin by transcription factors (TFs). Thus, detecting and characterizing direct interactions between HMEs and TFs are critical for understanding their function and specificity better. These studies would be more biologically relevant if performed in vivo within living tissues. Here, a protocol is described for visualizing interactions in plant leaves between a plant histone deubiquitinase and a plant transcription factor using fluorescence resonance energy transfer (FRET), which allows the detection of complexes between protein molecules that are within &#60;10 nm from each other. Two variations of the FRET technique are presented: SE-FRET (sensitized emission) and AB-FRET (acceptor bleaching), in which the energy is transferred non-radiatively from the donor to the acceptor or emitted radiatively by the donor upon photobleaching of the acceptor. Both SE-FRET and AB-FRET approaches can be adapted easily to discover other interactions between other proteins in planta.

Investigating Interactions Between Histone Modifying Enzymes and Transcription Factors in vivo by Fluorescence Resonance Energy Transfer

Fluorescence resonance energy transfer (FRET) is an imaging technique for detecting protein interactions in living cells. Here, a FRET protocol is presented to study the association of histone-modifying enzymes with transcription factors that recruit them to the target promoters for epigenetic regulation of gene expression in plant tissues.

Epigenetic regulation of gene expression is commonly affected by histone modifying enzymes (HMEs) that generate heterochromatic or euchromatic histone ...

Exploring Plasmodesmata Function: Confocal Microscopy of Targeted Proteins

Confocal Microscopy Analysis of Protein Sorting to Plasmodesmata in Nicotiana benthamiana

Plasmodesmata are membranous nanopores that connect the cytoplasm of adjacent plant cells and enable the cell-to-cell trafficking of nutrients, macromolecules, as well as invading viruses. Plasmodesmata play fundamental roles in the regulation of intercellular communication, contributing to plant development, environmental responses, and interactions with viral pathogens. Discovering plasmodesmal localization of plant or viral proteins could provide useful functional information about the protein and is important for understanding the mechanisms of plant-virus interactions. To facilitate these studies, we describe a protocol for confocal microscopy-based analysis of different plasmodesmal targeting proteins to select the best plasmodesmal marker for studying the virus-plasmodesmata interactions or plasmodesmal transport. Specifically, the analyses of these events are illustrated using the cell-to-cell movement protein (MP) of the Turnip vein-clearing virus (TVCV), the Arabidopsis Plasmodesmata-Localized Protein 5 (PDLP5) and Plasmodesmata Callose-Binding Protein 1 (PDCB1). The protein plasmodesmal localization data are analyzed in parallel with the global visualization of plasmodesmata using aniline blue staining of the sampled tissues. These approaches can be easily adapted to analyze the plasmodesmal localization of any cellular or pathogen proteins in planta.

Author Spotlight: Microscopic Analysis of Protein Localization at Plasmodesmata in Plants

This protocol describes the selection of optimal plasmodesmal markers for confocal microscopy-based analyses of protein targeting to plasmodesmata during virus-plasmodesmata interactions or plasmodesmal transport.