This work was supported by grants from the &#34;Shuguang Program&#34; of Shanghai Education Development Foundation and Shanghai Municipal Education Commission, the National Key Research and Development Program of China National Key R&amp;D Program of China (2018YFD0201500), the National Natural Science Foundation of China (no. 31571696 and 31660510), the Thousand Talents Program for Young Professionals of China, and the Science and Technology Commission of Shanghai Municipality (18DZ2260500).

NOTE: All steps of the procedure should be conducted at room temperature (RT).
CAUTION: Deposit all media containing pathogenic microbes, as well as the plants and plant tissue used in the assay, into the appropriate waste containers and autoclave before discarding.
1. Preparation of plasmid constructs containing putative effectors
<ol>
	<li>Select putative secreted effectors that are highly expressed during infection, as determined by RNA sequencing (RNA-Seq), an...

<ol>
	<li>Waterfield, N. 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=Rapid+Virulence+Annotation+(RVA):+identification+of+virulence+factors+using+a+bacterial+genome+library+and+multiple+invertebrate+hosts.">Rapid Virulence Annotation (RVA): identification of virulence factors using a bacterial genome library and multiple invertebrate hosts.</a> Proceedings of the National Academy of Sciences of the United States of America. 105 (41), 15967-15972 (2008).</li><li>Rovenich, H., Boshoven, J. C., Thomma, B. P. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Filamentous+pathogen+effector+functions:+of+pathogens,+hosts+and+microbiomes.">Filamentous pathogen effector functions: of pathogens, hosts and microbiomes.</a> Current Opinion in Plant Biology. 20, 96-103 (2014).</li><li>Varden, F. A., De la Concepcion, J. C., Maidment, J. H., Banfield, M. J. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Taking+the+stage:+effectors+in+the+spotlight.">Taking the stage: effectors in the spotlight.</a> Current Opinion in Plant Biology. 38, 25-33 (2017).</li><li>Lee, A. 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=Identifying+Pseudomonas+syringae+Type+III+Secreted+Effector+Function+via+a+Yeast+Genomic+Screen.">Identifying Pseudomonas syringae Type III Secreted Effector Function via a Yeast Genomic Screen.</a> G3: Genes, Genomes, Genetics. 9 (2), 535-547 (2019).</li><li>Toruno, T. Y., Stergiopoulos, I., Coaker, G. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Plant-Pathogen+Effectors:+Cellular+Probes+Interfering+with+Plant+Defenses+in+Spatial+and+Temporal+Manners.">Plant-Pathogen Effectors: Cellular Probes Interfering with Plant Defenses in Spatial and Temporal Manners.</a> Annual Review of Phytopathology. 54, 419-441 (2016).</li><li>Baulcombe, D. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=RNA+silencing+in+plants.">RNA silencing in plants.</a> Nature. 431 (7006), 356-363 (2004).</li><li>Pumplin, N., Voinnet, O. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=RNA+silencing+suppression+by+plant+pathogens:+defence,+counter-defence+and+counter-counter-defence.">RNA silencing suppression by plant pathogens: defence, counter-defence and counter-counter-defence.</a> Nature Reviews Microbiology. 11 (11), 745-760 (2013).</li><li>Csorba, T., Kontra, L., Burgyan, J. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Viral+silencing+suppressors:+Tools+forged+to+fine-tune+host-pathogen+coexistence.">Viral silencing suppressors: Tools forged to fine-tune host-pathogen coexistence.</a> Virology. 479-480, 85-103 (2015).</li><li>Johansen, L. K., Carrington, J. C. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Silencing+on+the+spot.+Induction+and+suppression+of+RNA+silencing+in+the+Agrobacterium-mediated+transient+expression+system.">Silencing on the spot. Induction and suppression of RNA silencing in the Agrobacterium-mediated transient expression system.</a> Plant Physiology. 126 (3), 930-938 (2001).</li><li>Powers, J. G., 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=A+versatile+assay+for+the+identification+of+RNA+silencing+suppressors+based+on+complementation+of+viral+movement.">A versatile assay for the identification of RNA silencing suppressors based on complementation of viral movement.</a> Molecular Plant-Microbe Interactions. 21 (7), 879-890 (2008).</li><li>Voinnet, O., Lederer, C., Baulcombe, D. C. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=A+viral+movement+protein+prevents+spread+of+the+gene+silencing+signal+in+Nicotiana+benthamiana.">A viral movement protein prevents spread of the gene silencing signal in Nicotiana benthamiana.</a> Cell. 103 (1), 157-167 (2000).</li><li>Deleris, 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=Hierarchical+action+and+inhibition+of+plant+Dicer-like+proteins+in+antiviral+defense.">Hierarchical action and inhibition of plant Dicer-like proteins in antiviral defense.</a> Science. 313 (5783), 68-71 (2006).</li><li>Li, W. X., 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=Interferon+antagonist+proteins+of+influenza+and+vaccinia+viruses+are+suppressors+of+RNA+silencing.">Interferon antagonist proteins of influenza and vaccinia viruses are suppressors of RNA silencing.</a> Proceedings of the National Academy of Sciences of the United States of America. 101 (5), 1350-1355 (2004).</li><li>Navarro, 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=A+plant+miRNA+contributes+to+antibacterial+resistance+by+repressing+auxin+signaling.">A plant miRNA contributes to antibacterial resistance by repressing auxin signaling.</a> Science. 312 (5772), 436-439 (2006).</li><li>Qiao, Y., 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=Oomycete+pathogens+encode+RNA+silencing+suppressors.">Oomycete pathogens encode RNA silencing suppressors.</a> Nature Genetics. 45 (3), 330-333 (2013).</li><li>Yin, C., 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=A+novel+fungal+effector+from+Puccinia+graminis+suppressing+RNA+silencing+and+plant+defense+responses.">A novel fungal effector from Puccinia graminis suppressing RNA silencing and plant defense responses.</a> New Phytologist. 222 (3), 1561-1572 (2019).</li><li>Zhang, P., 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+WY+domain+in+the+Phytophthora+effector+PSR1+is+required+for+infection+and+RNA+silencing+suppression+activity.">The WY domain in the Phytophthora effector PSR1 is required for infection and RNA silencing suppression activity.</a> New Phytologist. 223 (2), 839-852 (2019).</li><li>Petersen, T. N., Brunak, S., von Heijne, G., Nielsen, H. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=SignalP+4.0:+discriminating+signal+peptides+from+transmembrane+regions.">SignalP 4.0: discriminating signal peptides from transmembrane regions.</a> Nature Methods. 8 (10), 785-786 (2011).</li><li>Earley, K. W., 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=Gateway-compatible+vectors+for+plant+functional+genomics+and+proteomics.">Gateway-compatible vectors for plant functional genomics and proteomics.</a> Plant Journal. 45 (4), 616-629 (2006).</li><li>Woodman, M. E., Savage, C. R., Arnold, W. K., Stevenson, B. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Direct+PCR+of+Intact+Bacteria+(Colony+PCR).">Direct PCR of Intact Bacteria (Colony PCR).</a> Current Protocols in Microbiology. 42 (1), 1-7 (2016).</li><li>Cao, X., 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=Identification+of+an+RNA+silencing+suppressor+from+a+plant+double-stranded+RNA+virus.">Identification of an RNA silencing suppressor from a plant double-stranded RNA virus.</a> Journal of Virology. 79 (20), 13018-13027 (2005).</li><li>Burgyan, J., Havelda, Z. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Viral+suppressors+of+RNA+silencing.">Viral suppressors of RNA silencing.</a> Trends in Plant Science. 16 (5), 265-272 (2011).</li><li>Incarbone, M., Dunoyer, P. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=RNA+silencing+and+its+suppression:+novel+insights+from+in+planta+analyses.">RNA silencing and its suppression: novel insights from in planta analyses.</a> Trends in Plant Science. 18 (7), 382-392 (2013).</li><li>Martinez-Priego, L., Donaire, L., Barajas, D., Llave, C. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Silencing+suppressor+activity+of+the+Tobacco+rattle+virus-encoded+16-kDa+protein+and+interference+with+endogenous+small+RNA-guided+regulatory+pathways.">Silencing suppressor activity of the Tobacco rattle virus-encoded 16-kDa protein and interference with endogenous small RNA-guided regulatory pathways.</a> Virology. 376 (2), 346-356 (2008).</li></ol>

The authors have nothing to disclose.

RNA silencing is a key defense mechanism employed by plants to combat viral, bacterial, oomycete, and fungal pathogens. In turn, these microbes have evolved silencing suppressor proteins to counteract antiviral silencing, and these RSSs interfere with different steps of the RNA silencing pathway22,23. Several screening assays have been developed to identify RSSs10.
Here, we describe an improved protocol for scre...

Over the past two decades, acceleration in genome sequencing of microorganisms that cause plant diseases has led to an ever increasing knowledge gap between sequence information and the biological functions of encoded proteins1. Among the molecules revealed by sequencing projects are effector molecules that suppress innate immunity and facilitate host colonization; these factors are secreted by destructive plant pathogens, including bacteria, nematodes, and filamentous microbes. To respond to these threats, host plants have evolved novel receptors that recognize these effectors, enabling restoration of the immune response. Hence, effectors are subject to various selective pressures, leading to diversification of effector repertoires among pathogen lineages2. In recent years, putative effectors from plant pathogens have been shown to disrupt plant innate immunity by impeding host cellular processes to benefit the microbes in a variety of ways, including dysregulation of signaling pathways, transcription, intracellular transport, cytoskeleton stability, vesicle trafficking, and RNA silencing3,4,5. However, the vast majority of pathogen effectors, particularly those from filamentous pathogens, have remained enigmatic.
RNA silencing is a homology-mediated gene inactivation machinery that is conserved among eukaryotes. The process is triggered by long double-stranded RNA (dsRNA) and targets the homologous single-stranded RNA (ssRNA) in a sequence-specific manner, and it manipulates a wide range of biological processes, including antiviral defense6. To surmount innate immune responses of the host, some viruses have evolved to offset RNA silencing, including the ability to replicate inside intracellular compartments or escape from the silencing reorganized signal. Nevertheless, the most general strategy by which viruses protect their genomes against RNA silencing-dependent loss of gene function is to encode specific proteins that suppress RNA silencing7,8. Several mechanistically different approaches have been established to screen and characterize viral suppressors of RNA silencing (VSRs), including the co-infiltration of Agrobacterium tumefaciens cultures, transgenic plants expressing putative suppressors, grafting and cell culture9,10,11,12,13.
Each of these assays has advantages and disadvantages, and identifies VSRs in its own distinct manner. One of the most common approaches is based on the co-infiltration of individual A. tmuefaciens cultures harboring the potential viral protein and a reporter gene (typically green fluorescent protein [GFP]) on the Nicotiana benthamiana 16c plants constitutively expressing GFP under the control of the cauliflower mosaic virus 35S promoter. In the absence of an active viral silencing suppressor, GFP is identified as exogenous by the host cells and is silenced within 3 days post-infiltration (dpi). By contrast, if the viral protein possesses suppression activity, the expression level of GFP remains steady beyond 3&#8722;9 dpi9. This co-infiltration assay is simple and fast; however, it is neither highly stable nor sensitive. Nonetheless, the assay has identified numerous VSRs with diverse protein sequences and structures in many RNA viruses7,8.
Recently, several effector proteins that can inhibit the cellular RNA silencing activity have been characterized from bacterial, oomycete, and fungal plant pathogens14,15,16. These findings imply that RNA silencing suppression is a common strategy for facilitating infection that is used by pathogens in most kingdoms. In theory, many, if not all, of the effectors might encode RNA silencing suppressors (RSSs); to date, however, only a few have been identified, mainly due to the shortage of the reliable and general screening strategy. Moreover, suppressors of RNA silencing have not been investigated in the vast majority of plant pathogens17.
In this report, we present an optimized and general protocol for identifying plant pathogen effectors that can suppress local and systemic RNA silencing using the agro-infiltration assay. The foremost objective of this study was to emphasize the key aspects of the protocol and describe the steps in detail, thereby providing a screening assay that is suitable for almost all effectors of plant pathogens.

<table border="1" fo:keep-together.within-page="1" fo:keep-with-next.within-page="always">
	<tbody>
		<tr>
			<td>2-Morpholinoethanesulfonic Acid (MES)</td>
			<td>Biofroxx</td>
			<td>1086GR500</td>
			<td>Buffer</td>
		</tr>
		<tr>
			<td>2xTaq Master Mix</td>
			<td>Vazyme Biotech</td>
			<td>P112-AA</td>
			<td>PCR</td>
		</tr>
		<tr>
			<td>3-(N-morpholino) propanesulfonic acid (MOPS)</td>
			<td>Amresco</td>
			<td>0264C507-1KG</td>
			<td>MOPS Buffer</td>
		</tr>
		<tr>
			<td>Acetosyringone (AS)</td>
			<td>Sigma-Aldrich</td>
			<td>D134406-5G</td>
			<td>Induction of Agrobacterium</td>
		</tr>
		<tr>
			<td>Agar</td>
			<td>Sigma-Aldrich</td>
			<td>A1296-1KG</td>
			<td>LB medium</td>
		</tr>
		<tr>
			<td>Agarose</td>
			<td>Biofroxx</td>
			<td>1110GR100</td>
			<td>Electrophoresis</td>
		</tr>
		<tr>
			<td>Amersham Hybond -N+</td>
			<td>GE Healthcare</td>
			<td>RPN303 B</td>
			<td>Nothern blot</td>
		</tr>
		<tr>
			<td>Amersham Imager</td>
			<td>GE Healthcare</td>
			<td>Amersham Imager 600</td>
			<td>Image</td>
		</tr>
		<tr>
			<td>Bacto Tryptone</td>
			<td>BD Biosciences</td>
			<td>211705</td>
			<td>LB medium</td>
		</tr>
		<tr>
			<td>Bacto Yeast Extraction</td>
			<td>BD Biosciences</td>
			<td>212750</td>
			<td>LB medium</td>
		</tr>
		<tr>
			<td>Camera</td>
			<td>Nikon</td>
			<td>D5100</td>
			<td>Photography</td>
		</tr>
		<tr>
			<td>ChemiDoc MP Imaging System</td>
			<td>Bio-Rad</td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td>Chemiluminescent detection module component of dafa kits</td>
			<td>Thermo Fisher Scientific</td>
			<td>89880</td>
			<td>Luminescence detection</td>
		</tr>
		<tr>
			<td>Chloramphenicol</td>
			<td>Amresco</td>
			<td>0230-100G</td>
			<td>Antibiotics</td>
		</tr>
		<tr>
			<td>ClonExpress II One Step Cloning Kit</td>
			<td>Vazyme Biotech</td>
			<td>C112-01</td>
			<td>Ligation</td>
		</tr>
		<tr>
			<td>DIG Easy Hyb</td>
			<td>Sigma-Aldrich</td>
			<td>11603558001</td>
			<td>Hybridization buffer</td>
		</tr>
		<tr>
			<td>Easypure Plasmid Miniprep kit</td>
			<td>TransGen Biotech</td>
			<td>EM101-02</td>
			<td>Plasmid Extraction</td>
		</tr>
		<tr>
			<td>EasyPure Quick Gel Extraction Kit</td>
			<td>TransGen Biotech</td>
			<td>EG101-02</td>
			<td>Gel Extraction</td>
		</tr>
		<tr>
			<td>EDTA disodium salt dihydrate</td>
			<td>Amresco/VWR</td>
			<td>0105-1KG</td>
			<td>MOPS Buffer</td>
		</tr>
		<tr>
			<td>Electrophoresis Power Supply</td>
			<td>LiuYi</td>
			<td>DYY6D</td>
			<td>Nucleic acid electrophoresis.</td>
		</tr>
		<tr>
			<td>FastDigest EcoRV</td>
			<td>Thermo Fisher Scientific</td>
			<td>FD0304</td>
			<td>Vector digestion</td>
		</tr>
		<tr>
			<td>Gel Image System</td>
			<td>Tanon</td>
			<td>Tanon3500</td>
			<td>Image</td>
		</tr>
		<tr>
			<td>Gentamycin</td>
			<td>Amresco</td>
			<td>0304-5G</td>
			<td>Antibiotics</td>
		</tr>
		<tr>
			<td>Kanamycin Sulfate</td>
			<td>Sigma-Aldrich</td>
			<td>K1914</td>
			<td>Antibiotics</td>
		</tr>
		<tr>
			<td>LR Clonase II enzyme</td>
			<td>Invitrogen</td>
			<td>11791020</td>
			<td>LR reaction</td>
		</tr>
		<tr>
			<td>Nitrocellulose Blotting membrane 0.45um</td>
			<td>GE Healthcare</td>
			<td>10600002</td>
			<td>Northern</td>
		</tr>
		<tr>
			<td>NORTH2south biotin random prime dna labeling kit</td>
			<td>Thermo Fisher Scientific</td>
			<td>17075</td>
			<td>Biotin labeling</td>
		</tr>
		<tr>
			<td>PCR Thermal Cyclers</td>
			<td>Bio-Rad</td>
			<td>T100</td>
			<td>PCR</td>
		</tr>
		<tr>
			<td>Peat moss</td>
			<td>PINDSTRUP</td>
			<td>Dark Gold + clay</td>
			<td>Plants</td>
		</tr>
		<tr>
			<td>Peters Water-Soluble Fertilizer</td>
			<td>ICE</td>
			<td>Peter Professional 20-20-20</td>
			<td>Fertilizer</td>
		</tr>
		<tr>
			<td>Phanta Max Super-Fidelity DNA Polymerase</td>
			<td>Vazyme Biotech</td>
			<td>P505-d1</td>
			<td>Enzyme</td>
		</tr>
		<tr>
			<td>Rifampicin</td>
			<td>MP Biomedicals</td>
			<td>219549005</td>
			<td>Antibiotics</td>
		</tr>
		<tr>
			<td>RNA Gel Loading Dye (2X)</td>
			<td>Thermo Fisher Scientific</td>
			<td>R0641</td>
			<td>RNA Gel Loading Dye</td>
		</tr>
		<tr>
			<td>Sodium Acetate Hydrate</td>
			<td>Amresco/VWR</td>
			<td>0530-1KG</td>
			<td>MOPS Buffer</td>
		</tr>
		<tr>
			<td>Sodium Chloride</td>
			<td>Amresco</td>
			<td>0241-10KG</td>
			<td>LB medium</td>
		</tr>
		<tr>
			<td>Tri-Sodium citrate</td>
			<td>Amresco</td>
			<td>0101-1KG</td>
			<td>SSC Buffer</td>
		</tr>
		<tr>
			<td>Trizol Reagent</td>
			<td>Invitrogen</td>
			<td>15596018</td>
			<td>RNA isolation reagent</td>
		</tr>
		<tr>
			<td>UV lamp</td>
			<td>Analytik Jena</td>
			<td>UVP B-100AP</td>
			<td>Observation</td>
		</tr>
		<tr>
			<td>UVP Hybrilinker Oven</td>
			<td>Analytik Jena</td>
			<td>OV2000</td>
			<td>Northern</td>
		</tr>
	</tbody>
</table>

screening and identification of rna silencing suppressors from secreted effectors of plant pathogens

RNA silencing is an evolutionarily conserved, sequence-specific gene regulation mechanism in eukaryotes. Several plant pathogens have evolved proteins with the ability to inhibit the host plant RNA silencing pathway. Unlike virus effector proteins, only several secreted effector proteins have showed the ability to suppress RNA silencing in bacterial, oomycete, and fungal pathogens, and the molecular functions of most effectors remain largely unknown. Here, we describe in detail a slightly modified version of the co-infiltration assay that could serve as a general method for observing RNA silencing and for characterizing effector proteins secreted by plant pathogens. The key steps of the approach are choosing the healthy and fully developed leaves, adjusting the bacteria culture to the appropriate optical density (OD) at 600 nm, and observing green fluorescent protein (GFP) fluorescence at the optimum time on the infiltrated leaves in order to avoid omitting effectors with weak suppression activity. This improved protocol will contribute to rapid, accurate, and extensive screening of RNA silencing suppressors and serve as an excellent starting point for investigating the molecular functions of these proteins.

Above, we describe the step-by-step procedure for an improved screening assay for assessing the RSS activity of P. sojae RxLR effectors. Altogether, the experiment takes 5&#8722;6 weeks. Subsequently, the RSSs identified by the assay can be further characterized in terms of function and molecular mechanism. As an example of our approach, we used the P. sojae RxLR effecto Phytophthora suppressor of RNA silencing 1 (PSR1), which is secreted and delivered into host cells th...

Watch this Scientific Journal Video about Screening and Identification of RNA Silencing Suppressors from Secreted Effectors of Plant Pathogens at JoVE.com

Screening and Identification of RNA Silencing Suppressors from Secreted Effectors of Plant Pathogens

Here, we present a modified screening method that can be extensively used to quickly screen RNA silencing suppressors in plant pathogens.

RNA silencing is an evolutionarily conserved, sequence-specific gene regulation mechanism in eukaryotes. Several plant pathogens have evolved proteins ...

This method can help to answer key questions about how to screen the RNA silencing suppressors secreted by plant pathogens. The main advantage of this technique is to provide a rapid, accurate and extensive screening assay for RNA silencing suppressors identification. Prepare potting soil mixes consisting of 50%peat moss, 30%perlite, and 20%vermiculite and autoclave at 120 degrees Celsius for 20 minutes.Soak the autoclaved soil mixes with plant fertilizer solution at one gram per liter and subpackage them into smaller pots stored in a larger tray. Sow one or two seeds of Nicotiana bethamiana 16c onto the soil surface of each pot. Cover the tray with a plastic dome and allow the seeds to germinate.Place the tray under light and temperature-controlled growth chambers with a temperature of 23 to 25 degrees Celsius, 50 to 60%relative humidity, and a long day photoperiod. After three to four days, the seeds germinate. Take the plastic dome off and allow the seedlings to grow under the same conditions used for the germination step.Every two to three days, add an appropriate amount of water keeping the soil moist but not soaking. Every 10 days, add fertilizer to promote further growth. Maintain Nicotiana bethamiana 16c plants under normal conditions until the plants have at least five fully developed true leaves with no visible axillary or flower buds and the leaves have a healthy green appearance.Use 10 to 14-day-old Nicotiana bethamiana 16c plants for systemic RNA silencing assays and three to four-week-old leaves of Nicotiana bethamiana 16c for local RNA silencing assays. Use a tip to pick a positive colony from the LB plate and inoculate the cells into a glass tube containing five milliliters of LB medium supplemented with 50 micrograms per milliliter Kanamycin and 50 micrograms per milliliter Rifampicin. Grow the cells at 30 degrees Celsius with shaking at 200 RPM for 24 to 48 hours.Transfer 100 microliters of the culture into five milliliters of LB medium supplemented with the same antibiotics, 10 millimolar MES at pH 5.6, and 20 micromolar AS.Grow the bacteria at 30 degrees Celsius with shaking at 200 RPM for 16 to 20 hours. Centrifuge the cells at 4, 000 times g for 10 minutes. Discard the supernatant and resuspend the pellet in two milliliters of 10 millimolar magnesium chloride buffer.Repeat the wash to ensure the complete removal of antibiotics. Determine the density of the Agrobacterium culture by measuring the optical density at 600 nanometers. Adjust the cell culture with 10 millimolar magnesium chloride buffer to an OD 600 of 1.5 to 2.0.Add 10 millimolar MES at pH 5.6 and 150 micromolar AS to the final suspension culture and incubate the cells at room temperature for at least three hours without shaking. Mix equal volumes of an Agrobacterium culture containing 35S green fluorescent protein with an Agrobacterium culture containing 35S cucumber mosaic virus suppressor 2b, putative effector or empty vector. Using a one milliliter needleless syringe, carefully and slowly infiltrate the mixed Agrobacterium suspensions on the abaxial sides of Nicotiana bethamiana 16c leaves.Remove the remaining bacterial suspension from the leaves with soft tissue wipes and circle the margins of the infiltrated patches with a marker pen. Three to four days post-infiltration, use a long wave ultraviolet lamp to visually detect GFP fluorescence in the infiltrated patches of leaves. Two weeks post-infiltration, use the lamp to detect newly grown leaves of the whole plant for systemic RNA silencing.To isolate the total RNA from the leaf tissue at four to seven days post-infiltration, collect the leaf tissues from the infiltrated Nicotiana bethamiana 16c patches into a mortar. Place liquid nitrogen into the mortar and grind the tissue into a fine powder with a grinding rod and transfer the powder to a sterile two milliliter tube. Immediately add the RNA isolation reagent at the volume of one milliliter per 100 milligrams of tissue to the sample tube in a hood, vortex vigorously to homogenate, and incubate at room temperature for five minutes.Add chloroform at the volume of 200 microliters per one milliliter of RNA isolation reagent to each tube in the hood, shake vigorously for 15 seconds, and incubate at room temperature for five minutes. Centrifuge the homogenate at 12, 000 times g for 15 minutes at four degrees Celsius. Transfer the supernatant into a new RNase-free tube and discard the pellet.Add 0.7 volume of isopropanol to the supernatant, gently invert several times, and incubate the mixture at room temperature for 10 minutes. Precipitate the RNA pellet by centrifugation at 12, 000 times g for 15 minutes at four degrees Celsius. Discard the supernatant.Wash the pellet with 70%ethanol and air dry the pellet in a hood. Dissolve the RNA in diethyl pyrocarbonate treated water by incubating in a 65 degrees Celsius water bath for 10 to 20 minutes. To perform Northern blot analysis of GFP messenger RNA levels, prepare a 1.2%formaldehyde denaturing agarose gel in 1X MOPS running buffer.Mix the RNA one-to-one with RNA loading dye and denature the RNA by incubation at 65 degrees Celsius for 10 minutes. Immediately chill the denatured samples on ice for one minute. With a pipette, load the samples into the wells of the gel and electrophorese at 100 volts for 50 minutes until the RNA is well separated.Rinse the gel into 20X saline sodium citrate buffer to remove the formaldehyde. Perform capillary transfer overnight by setting up 20X saline sodium citrate buffer, one layer of paper towel, two layers of wet Whatman paper, one layer of gel, one layer of nylon membrane, two layers of wet Whatman paper, two layers of dry Whatman paper, one glass plate, and a weight. In the morning, the RNA in the gel is transferred to the nylon membrane.Soak the membrane in 2X saline sodium citrate and fix the RNA to the membrane by exposing the wet membrane to UV crosslinking. Proceed according to the manuscript. Fully developed leaves of three to four-week-old Nicotiana bethamiana 16c plants were co-infiltrated in patches with Agrobacterium mixtures carrying 35S GFP.At four days post-infiltration, GFP fluorescence of the infiltrated area was imaged under natural light and long wave UV light. Northern blot revealed that GFP messenger RNA accumulated higher in the leaves expressing 35S GFP plus 35S CMV2b or 35S GFP plus 35S PSR1 than in the leaves expressing 35S GFP plus EV.Agroinfiltration assay was performed to evaluate the spread of the silencing signal in the leaves of two-week-old Nicotiana bethamiana 16c seedlings. At 14 days post-infiltration, more than 98%of the EV exhibited no obvious GFP signaling in systemic leaves.Whereas both CMV2b and PSR1 efficiently inhibited the systemic spread of the silencing signal. GFP fluorescence was observed in about 80%of co-infiltrated plants and in the remaining 20%of infiltrated plants with only a few red veins appeared in newly emerged leaves. This technique paves the way for researchers to identify novel RNA silencing suppressors secreted by many plant pathogens.The combination of plants and the proper OD is the most important thing to remember when attempting this procedure. Following this procedure, the functional characterization of the RNA silencing suppressor can be done to explore the mechanism of how these suppressors press the host RNA silencing and what is the output. Please wear the safety goggles when you infiltrate plants and also wear the latex gloves during all the experiment steps.

screening-identification-rna-silencing-suppressors-from-secreted

Research

JoVE Journal

Genetics

6.2K 조회수.  Shanghai Normal University. 이 방법은 식물 병원체에 의해 분비된 RNA 침묵 억제제를 검열하는 방법에 대한 중요한 질문에 대답하는 것을 도울 수 있습니다. 이 기술의 주요 장점은 RNA 침묵 억제제 식별에 대한 신속하고 정확하며 광범위한 스크리닝 분석법을 제공하는 것입니다. 20분 동안 120도에서 50%의 토탄 이끼, 30%의 펄라이트, 20%의 버미쿨라이트 및 오토클레이브로 구성된 포팅 토양 믹스를 준비합?...