Name: screening and identification of rna silencing suppressors from secreted effectors of plant pathogens
Uploaded: 2020-02-03T14:00:00
Description: Watch this Scientific Journal Video about Screening and Identification of RNA Silencing Suppressors from Secreted Effectors of Plant Pathogens at JoVE.com

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>
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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>

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 ...

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The intimate interaction between plant host and associated microorganisms is crucial in determining plant fitness, and can foster improved tolerance to ...

Generation of Cancer Cell Clones to Visualize Telomeric Repeat-containing RNA TERRA Expressed from a Single Telomere in Living Cells

Telomeres are transcribed, giving rise to telomeric repeat-containing long noncoding RNAs (TERRA), which have been proposed to play important roles in ...

Identification of Footprints of RNA:Protein Complexes via RNA Immunoprecipitation in Tandem Followed by Sequencing (RIPiT-Seq)

Identification of Footprints of RNA:Protein Complexes via RNA Immunoprecipitation in Tandem Followed by Sequencing RIPiT-Seq

RNA immunoprecipitation in tandem (RIPiT) is a method for enriching RNA footprints of a pair of proteins within an RNA:protein (RNP) complex. RIPiT ...

Identification of Circular RNAs using RNA Sequencing

Circular RNAs (circRNAs) are a class of non-coding RNAs involved in functions including micro-RNA (miRNA) regulation, mediation of protein-protein ...

A FACS-based Protocol to Isolate RNA from the Secondary Cells of Drosophila Male Accessory Glands

A FACS-based Protocol to Isolate RNA from the Secondary Cells of Drosophila Male Accessory Glands

To understand the function of an organ, it is often useful to understand the role of its constituent cell populations. Unfortunately, the rarity of ...