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 pl...

<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.

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	<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 ...

The overall goal of this procedure is to quantitatively detect protein-protein interactions in a transient expression system. This measure can help answer key questions in quan-signal transaction fields such as how to quantitatively monitor our protein protein directions after a chemical or environmental treatment. The main advantage of this technic is that it uses a luminometer or a CCD camera to detect the luciferous activity, which represents the protein protein direction intensity so the results are more accurate.To begin this procedure, add one milliliter of a solution containing five percent sodium hypochlorite and zero point one percent triton x one hundred to a one point five milliliter microcentrifuge tube containing seeds. Let the solution rest for five minutes to sterilize the seeds. Then, wash the seeds with sterile water five times.Suspend the washed seeds in two hundred microliters of steril water. Using fine tips, carefully place individual seeds onto the surface of plated MS agar medium. Store the plates at four degrees Celsius for three days to synchronize germination.After this, keep medium plates under normal growth conditions for ten days. Transfer the germinating seedlings into soil, making sure not to damage the roots. Cover the tray with a transparent plastic cover overnight to maintain humidity.Grow plants in a controlled growth room for seven weeks, when they'll be ready for agrobacterium tumefaciens infiltration. To begin, deliver one hundred and fifty nanograms of plasmids into the a-tumefaciens competent cell strain GV3101. Place the tubes containing the a-tumefaciens culture in a shaker, and incubate for four hours.Using a glass rod, transfer the culture from the tubes to LB mediums. Culture a-tumefaciens and LB agar medium at 28 degrees celsius for four days. Next, prepare to inoculate a single a-tumefaciens colony from each plate into its own tube containing three milliliters of LB liquid medium.Shake at 280 RBM at 28 degrees Celsius for 24 hours to propagate the culture. Then, transfer 75 microliters of the bacterial culture into 15 milliliters of fresh LB liquid medium containing 15 micrograms per milliliter of kanamycin and 50 micrograms per milliliter of rifampicin. Culture the bacteria at 220 RPM at 30 degrees Celsius for approximately 8 hours until OD600 is between 0.5 to 1.After this, transfer the culture to 15 milliliters centrifuge tubes. Centrifuge at 4000 times gravity and four degrees Celsius for 15 minutes. Discard the supernatant and resuspend the pallet in 15 milliliters of transformation solution.Centrifuge at 4000 times gravity and 4 degrees Celsius for 15 minutes. Then, repeat the suspension and centrifugation step once more. Discard the supernatant and resuspend the pallet in 5 milliliters of transformation solution.Let the resuspended pallet rest for two hours at room temperature in dark conditions. Then, either add transformation solution into the OD600 is 0.5 or combine two samples with equal volume for testing paired protein interactions. Using a one milliliter needle of syringe, infiltrate suspended cells into the fourth to seventh leaves.After this, immediately cover the plants with a black plastic cover for 12 hours. Firstly, plants should be very healthy to ensure success. Secondly, make sure not to damage any leaves during the infiltration process.Keep the tray in darkness for 12 hours. Then grow the plants under normal conditions for 2 to 4 days before detecting the luciferase activity. To begin the imaging method, detach an infiltrated leaf.Place the entire leaflet on a plate of MS agar medium. Using a 50 milliliter spray bottle, spray luciferon working buffer onto the leafs adaxial side. Then, keep in the dark for 5 minutes to quench the chlorophyll autofluorescence.Use a lower light cooled CCD imagine apparatus cooled to negative 30 degrees Celsius to capture images with a light filled exposure time of 50 milliseconds, and luminescence detection time of 1 minute. After this, cut out leaf fragments from the infiltration area of the N-benthamiana leaves. Immerse the fragments in 100 microliters of deionized water in the wells of 96-well white plate.Add ten microliters of luciferon working buffer. Let the plate rest 5 minutes. Then, perform any desired specific treatment to study protein interaction dynamics, and measure the luminescence directly with a commercial luminometer.Shown here is the demonstration of luciferous activity to represent of COP 1 SPA 1 interactions. The luciferous activity, which is detected by luminescence, is imaged by CCD camera. COP 1 SPA 1 interactions are seen to result in copper mutation of functional luciferase.The luciferase activity under Jasmine 8 treatment over time is then determined. COP 1 SPA 1 interactions represented by luciferase activity are seen to gradually decline in darkness. Treatment with Jasmine 8 further reduces these interactions.Once mastered, this technic can be done in 1 week, after the plants are ready if it's performed properly. While attempting this procedure, it is important to remember to maintain healthy plants. Infiltrate leaves carefully and include controls properly.After it's development, this technic paves the way for researchers in the field of signal transactions to explore protein protein interaction dynamics in a rapid way. After watching this video, you should have a good understanding of how to grow tobacco plants, infiltrate agrobacterias into tobacco leaves, and to detect luciferous activities.

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13.6K Views.  Nanjing Normal University. The overall goal of this procedure is to quantitatively detect protein-protein interactions in a transient expression system. This measure can help answer key questions in quan-signal transaction fields such as how to quantitatively monitor our protein protein directions after a chemical or environmental treatment. The main advantage of this technic is that it uses a luminometer or a CCD camera to detect the luciferous activity, which represents the protein protein direction intensity so the ...