Name: high-throughput identification of resistance to pseudomonas syringae pv. tomato in tomato using seedling flood assay
Uploaded: 2020-03-10T14:00:00
Description: Watch this Scientific Journal Video about High-Throughput Identification of Resistance to Pseudomonas syringae pv. Tomato in Tomato using Seedling Flood Assay at JoVE.com

We thank Jamie Calma for testing the effect of media volume on disease or resistance outcomes. We thank Dr. Ma&#235;l Baudin and Dr. Karl J. Scheiber from the Lewis Lab for providing constructive comments and suggestions on the manuscript. Research on plant immunity in the Lewis laboratory was supported by the USDA ARS 2030-21000-046-00D and 2030-21000-050-00D (JDL), and the NSF Directorate for Biological Sciences IOS-1557661 (JDL).

1. Preparation and use of biosafety cabinet
<ol>
	<li>Wipe down biosafety cabinet with 70% ethanol.</li>
	<li>Close the sash and turn on the ultraviolet light in the biosafety cabinet for 15 min.</li>
	<li>After 15 min, turn off the ultraviolet light in the biosafety cabinet. Lift the sash and turn on the blower for 15 min.</li>
	<li>Wipe all items to be used in the biosafety cabinet with 70% ethanol prior to putting the items into the sterilized cabinet.</li>
	<li>Clean gloves or bare hands with 70% ethanol before wor...

<ol>
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A protocol for flood inoculation with PstDC3000 or Pst19 optimized to detect resistance to these bacterial strains in tomato seedlings is described. There are several critical parameters for optimal results in the seedling resistance assay, including bacterial concentration and surfactant concentration, which were empirically determined22. For PstDC3000, the optical density was optimized to achieve complete survival on a resistant cultivar containing the Pto/Prf...

An erratum was issued for:&#160;<a href="https://www.jove.com/t/60805">High-Throughput Identification of Resistance to Pseudomonas syringae pv. Tomato in Tomato using Seedling Flood Assay</a>. The Introduction, Protocol, Representative Results and Discussion&#160;sections were&#160;updated.

Erratum: High-Throughput Identification of Resistance to Pseudomonas syringae pv. Tomato in Tomato using Seedling Flood Assay

Pseudomonas syringae is a Gram-negative pathogenic bacterium that infects a wide range of plant hosts. Bacteria enter the host plant through the stomata or physical wounds and proliferate in the apoplast1. Plants have evolved a two-tiered immune response to protect against infection by bacterial pathogens. The first level occurs at the plant cell surface, where pattern recognition receptors on the plant cell membrane perceive highly conserved pathogen-associated molecular patterns (PAMPs) in a process called PAMP-triggered immunity (PTI)2. During this process, the host plant upregulates defense response pathways, including deposition of callose to the cell wall, closure of stomata, production of reactive oxygen species, and induction of pathogenesis-related genes.
Bacteria can overcome PTI by utilizing a type III secretion system to deliver proteins, called effectors, directly into the plant cell3. Effector proteins commonly target components of PTI and promote pathogen virulence4. The second tier of plant immunity occurs within the plant cell upon recognition of the effector proteins. This recognition is dependent on resistance genes, which encode nucleotide-binding site leucine-rich repeat containing receptors (NLRs). NLRs are capable of either recognizing effectors directly or recognizing their activity on a virulence target or decoy5. They then trigger a secondary immune response in a process called effector-triggered immunity (ETI), which is often associated with a hypersensitive response (HR), a form of localized cell death at the site of infection6. In contrast to gene-for-gene resistance associated with ETI, plants can exhibit quantitative partial resistance, which is dependent on the contribution of multiple genes7.
P. syringae pv. tomato (Pst) is the causal agent of bacterial speck on tomato and is a persistent agricultural problem. Predominant strains in the field have typically been Pst race 0 strains that express either or both of the type III effectors AvrPto and AvrPtoB. DC3000 (PstDC3000) is a representative race 0 strain and a model pathogen that can cause bacterial speck in tomato. To combat bacterial speck disease, breeders introgressed the Pto [P. syringae pv. tomato]/Prf [Pto resistance and fenthion sensitivity] gene cluster from the wild tomato species Solanum pimpinellifolium into modern cultivars8,9. The Pto gene encodes a serine-threonine protein kinase that, together with the Prf NLR, confer resistance to PstDC3000 via recognition of the effectors AvrPto and AvrPtoB10,11,12,13,14. However, this resistance is ineffective against emerging race 1 strains, allowing for their rapid and aggressive spread in recent years15,16. Race 1 strains evade recognition by the Pto/Prf cluster, because AvrPto is either lost or mutated in these strains, and AvrPtoB appears to accumulate minimally15,17,18.
Wild tomato populations are important reservoirs of natural variation for Pst resistance and have previously been used to identify potential resistance loci19,20,21. However, current screens for pathogen resistance utilize 4&#8211;5-week-old adult plants20,21. Therefore, they are limited by growth time, growth chamber space, and relatively small sample sizes. To address the limitations of conventional approaches, we developed a high-throughput tomato P. syringae resistance assay using 10-day-old tomato seedlings22. This approach offers several advantages over using adult plants: namely, shorter growth time, reduced space requirements, and higher throughput. Furthermore, we have demonstrated that this approach faithfully recapitulates disease resistance phenotypes observed in adult plants22.
In the seedling flood assay described in this protocol, tomato seedlings are grown on Petri dishes of sterile Murashige and Skoog (MS) media for 10 days and then are flooded with an inoculum containing the bacteria of interest and a surfactant. Following flooding, seedlings can be quantitatively evaluated for disease resistance via bacterial growth assays. Additionally, seedling survival or death can act as a discrete resistance or disease phenotype 7&#8211;14 days after flooding. This approach offers a high-throughput alternative for screening large numbers of wild tomato accessions for resistance to Pst race 1 strains, such as Pst strain 19 (Pst19), and can easily be adapted to other bacterial strains of interest.

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			<td>3M Tape Micropore 1/2&#34; x 10 YD CS 240 (1.25 cm x 9.1 m)</td>
			<td>VWR International</td>
			<td>56222-182</td>
			<td></td>
		</tr>
		<tr>
			<td>3mm borosilicate glass beads</td>
			<td>Friedrich &#38; Dimmock</td>
			<td>GB3000B</td>
			<td></td>
		</tr>
		<tr>
			<td>Bacto peptone</td>
			<td>BD</td>
			<td>211677</td>
			<td></td>
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		<tr>
			<td>Bacto agar</td>
			<td>BD</td>
			<td>214010</td>
			<td></td>
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			<td>Biophotometer Plus</td>
			<td>Eppendorf</td>
			<td>E952000006</td>
			<td></td>
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			<td>Biosafety cabinet, class II type A2</td>
			<td></td>
			<td></td>
			<td></td>
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			<td>BRAND Disposable Plastic Cuvettes, Polystyrene</td>
			<td>VWR International</td>
			<td>47744-642</td>
			<td></td>
		</tr>
		<tr>
			<td>Chenille Kraft Flat Wood Toothpicks</td>
			<td>VWR International</td>
			<td>500029-808</td>
			<td></td>
		</tr>
		<tr>
			<td>cycloheximide</td>
			<td>Research Products International</td>
			<td>C81040-5.0</td>
			<td></td>
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		<tr>
			<td>Dibasic potassium phosphate anhydrous, ACS grade</td>
			<td>Fisher Scientific</td>
			<td>P288-500</td>
			<td></td>
		</tr>
		<tr>
			<td>Dimethylformamide</td>
			<td></td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td>Dissecting microscope (Magnification of at least 10x)</td>
			<td></td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td>Ethanol - 190 Proof</td>
			<td></td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td>Falcon polystyrene 96 well microplates, flat-bottom</td>
			<td>Fisher Scientific</td>
			<td>08-772-3</td>
			<td></td>
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			<td>Glass Alcohol Burner Wick</td>
			<td>Fisher Scientific</td>
			<td>S41898A / No. W-125</td>
			<td></td>
		</tr>
		<tr>
			<td>Glass Alcohol Burners</td>
			<td>Fisher Scientific</td>
			<td>S41898 / No. BO125</td>
			<td></td>
		</tr>
		<tr>
			<td>Glycerol ACS reagent</td>
			<td>VWR International</td>
			<td>EMGX0185-5</td>
			<td></td>
		</tr>
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			<td>Kimberly-Clark&#8482; Kimtech Science&#8482; Kimwipes&#8482; Delicate Task Wipers</td>
			<td>Fisher Scientific</td>
			<td>06-666-A</td>
			<td></td>
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			<td>Magnesium chloride, ACS grade</td>
			<td>VWR International</td>
			<td>97061-356</td>
			<td></td>
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			<td>Magnesium sulfate heptahydrate, ACS grade</td>
			<td>VWR International</td>
			<td>97062-130</td>
			<td></td>
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			<td>Microcentrifuge tubes, 1.5 mL</td>
			<td></td>
			<td></td>
			<td></td>
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			<td>Microcentrifuge tubes, 2.2 mL</td>
			<td></td>
			<td></td>
			<td></td>
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			<td>Mini Beadbeater-96, 115 volt</td>
			<td>Bio Spec Products Inc.</td>
			<td>1001</td>
			<td></td>
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		<tr>
			<td>Murashige &#38; Skoog, Basal Salts</td>
			<td>Caisson Laboratories, Inc.</td>
			<td>MSP01-50LT</td>
			<td></td>
		</tr>
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			<td>Pipet-Lite XLS LTS 8-CH Pipet 20-200uL</td>
			<td>Rainin</td>
			<td>L8-200XLS</td>
			<td></td>
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			<td>Pipet-Lite XLS LTS 8-CH Pipet 2-20uL</td>
			<td>Rainin</td>
			<td>L8-20XLS</td>
			<td></td>
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			<td>Polystyrene 100mm x 25mm sterile petri dish</td>
			<td>VWR International</td>
			<td>89107-632</td>
			<td></td>
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			<td>Polystyrene 150mm x 15mm sterile petri dish</td>
			<td>Fisher Scientific</td>
			<td>FB08-757-14</td>
			<td></td>
		</tr>
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			<td>Polystyrene 150x15mm sterile petri dish</td>
			<td>Fisher Scientific</td>
			<td>08-757-148</td>
			<td></td>
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			<td>Pure Bright Germicidal Ultra Bleach 5.7% Available Chlorine (defined as 100% bleach)</td>
			<td>Staples</td>
			<td>1013131</td>
			<td></td>
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			<td>Rifampicin</td>
			<td>Gold Biotechnology</td>
			<td>R-120-25</td>
			<td></td>
		</tr>
		<tr>
			<td>Silwet L-77 (non-ionic organosilicone surfactant co-polymer C13H34O4Si3 surfactant)</td>
			<td>Fisher Scientific</td>
			<td>NCO138454</td>
			<td></td>
		</tr>
		<tr>
			<td>Tips LTS 20 &#956;L 960/10 GPS-L10</td>
			<td>Rainin</td>
			<td>17005091</td>
			<td></td>
		</tr>
		<tr>
			<td>Tips LTS 250 &#956;L 960/10 GPS-L250</td>
			<td>Rainin</td>
			<td>17005093</td>
			<td></td>
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		<tr>
			<td>VWR dissecting forceps fine tip, 4.5&#34;</td>
			<td>VWR International</td>
			<td>82027-386</td>
			<td></td>
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high-throughput identification of resistance to pseudomonas syringae pv. tomato in tomato using seedling flood assay

Tomato is an agronomically important crop that can be infected by Pseudomonas syringae, a Gram-negative bacterium, resulting in bacterial speck disease. The tomato-P. syringae pv. tomato pathosystem is widely used to dissect the genetic basis of plant innate responses and disease resistance. While disease was successfully managed for many decades through the introduction of the Pto/Prf gene cluster from Solanum pimpinellifolium into cultivated tomato, race 1 strains of P. syringae have evolved to overcome resistance conferred by the Pto/Prf gene cluster and occur worldwide.
Wild tomato species are important reservoirs of natural diversity in pathogen recognition, because they evolved in diverse environments with different pathogen pressures. In typical screens for disease resistance in wild tomato, adult plants are used, which can limit the number of plants that can be screened due to their extended growth time and greater growth space requirements. We developed a method to screen 10-day-old tomato seedlings for resistance, which minimizes plant growth time and growth chamber space, allows a rapid turnover of plants, and allows large sample sizes to be tested. Seedling outcomes of survival or death can be treated as discrete phenotypes or on a resistance scale defined by amount of new growth in surviving seedlings after flooding. This method has been optimized to screen 10-day-old tomato seedlings for resistance to two P. syringae strains and can easily be adapted to other P. syringae strains.

Detection of PtoR-mediated immunity in cultivars and isogenic lines using the seedling resistance assay 
Figure 5 shows representative results for Moneymaker-PtoR and Moneymaker-PtoS cultivars 7&#8211;10 days after flooding with PstDC3000. Prior to infection, 10-day-old seedlings displayed fully emerged and expanded cotyledons and emerging first true leaves. The seedlings were flooded with 10 mM MgCl2 + 0.015% surfactant as...

Watch this Scientific Journal Video about High-Throughput Identification of Resistance to Pseudomonas syringae pv. Tomato in Tomato using Seedling Flood Assay at JoVE.com

High-Throughput Identification of Resistance to Pseudomonas syringae pv. Tomato in Tomato using Seedling Flood Assay

The seedling flood assay facilitates rapid screening of wild tomato accessions for the resistance to the Pseudomonas syringae bacterium. This assay, used in conjunction with the seedling bacterial growth assay, can assist in further characterizing the underlying resistance to the bacterium, and can be used to screen mapping populations to determine the genetic basis of resistance.

High-Throughput Identification of Resistance to Pseudomonas syringae pv. Tomato in Tomato using Seedling Flood Assay

Tomato is an agronomically important crop that can be infected by Pseudomonas syringae, a Gram-negative bacterium, resulting in bacterial speck disease. ...

This high throughput protocol allows rapid screening of tomato seedlings from wild accessions to the bacterial pathogen Pseudomonas syringae. The seedling flood assay minimizes plant growth time and growth chamber needs, allows rapid turnover of plants, and allows large sample sizes to be tested. This assay is a powerful tool that can be used to screen for resistance in wild accessions and other lines with complex genetic backgrounds.The protocol provides specific directions for flood innoculation of two Pseudomonas syringae strains. However, it is versatile and can be modified to detect host resistance to other bacterial pathogens. Demonstrating the procedure will be Yana Hasan, a research specialist in my laboratory.Begin by growing the tomato seedlings. Place tomato seeds in a 2.2 milliliter microcentrifuge tube and add two milliliters of 50%bleach solution. Rock the tube for 25 minutes then remove the bleach solution with a pipette.Add two milliliters of ultra pure water and wash the seeds by inverting the tube five times. Aspirate the liquid from the tube, and repeat the wash four more times. After the final wash, add two milliliters of ultra-pure water and pour the seeds into a sterile Petri dish.Sterilize forceps by flaming them in ethanol then use them to transfer five to seven seeds onto a 100 by 25 milliliter plate with 0.5 XMS plus 0.8 percent agar media. Seal the edges of the plate with surgical tape. Ensure that the plates are stacked flat and face up.Stratify the sterilized seeds at four degrees Celsius in the dark for at least three days to synchronize germination. After three days, vertically orient the plates so that the roots will grow down along the surface of the plate and the line of seeds is oriented horizontally. Transfer the seeds to a growth chamber set to 22 degrees Celsius with a 16-hour light, 8-hour dark cycle.Grow the seedlings for ten days in the chamber, at which point they will typically display fully emerged and expanded cotyledons and emerging first true leaves. Streak fresh bacteria onto appropriate KB agar with a flat, sterile toothpick. For PstT1, incubate the plate at 28 degrees Celsius for 48 hours prior to using the bacteria in the flood experiment.To prepare the inoculum, aseptically resuspend the bacteria in sterile, ten millimolar magnesium chloride to an optical density of 0.1. Then make two serial dilutions to obtain a working concentration with an OD600 of 0075. Also prepare a one to ten dilution of non-ionic organosilicone surfactant copolymer in ten millimolar magnesium chloride.Vortex it and add it to the bacteria, swirling the tube to mix. Transfer the plates with the ten-day-old seedlings from the growth chamber to the biosafety cabinet and remove the surgical tape. Then transfer six milliliters of inoculum to each plate.Gently push the seedlings into the inoculum with a pipette tip and start a timer for three minutes. Hold one plate in each hand and tilt the front of the plate down to submerge the cotyledons and leaves of the seedlings. Swish the inoculum side to side five to seven times, then tip the plates back to cover the roots with the inoculum.Tilt the plates down again and repeat the cycle for a total of three minutes. Pour the inoculum off the plates, set them down on a flat surface, and pour off any residual inoculum for a second time. Re-wrap the plates and place them back in the growth chamber.Moneymaker-PtoR and Moneymaker-PtoS cultivars were flooded with PSTDC3000 and phenotyped seven to ten days after flooding. Moneymaker-PtoR seedlings carry the PtoPRF gene cluster and were resistant to the PSTDC3000. While near-isogenic Moneymaker-PtoS seedlings, which cannot recognize the PSTDC3000 effectors AVRPto or AVRPto-B died quickly, within seven days after flooding.Ten day old seedlings were flooded with PstT1 and phenotyped at least ten days after flooding. Susceptible accessions were dead, had brown apical meristems and lacked new growth. In contrast, resistant seedlings displayed a high level of new green growth and survived infection with PstT1.Bacterial growth assays were carried out to quantitatively confirm PstT1 resistance and Solanum NeoRici LA1329. There was a 1.7 log difference in bacterial growth between resistant and susceptible LA1329 and a 1.6 log difference between resistant LA1329 and Moneymaker-PtoS, which correlated with the phenotypic results. When performing this assay, the most important things to remember are to pay close attention to aseptic technique throughout the protocol and ensure that all seedlings on the plate are thoroughly flooded.Be sure to autoclave infected plant tissue and bacteria and dispose of materials in accordance with appropriate regulations.

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