Intra-strain Elicitation and Suppression of Plant Immunity by Ralstonia solanacearum Type-III Effectors in Nicotiana benthamiana

For the development of pathogen-informed breeding strategies, identifying the microbial genes involved in interactions with the plant is a critical step. To identify type III effector (T3E) repertoires associated with virulence of the bacterial wilt pathogen Ralstonia solanacearum on Solanaceous crops, we used an original association genetics approach combining DNA microarray data and pathogenicity data on resistant eggplant, pepper, and tomato accessions. From this first screen, 25 T3Es were further full-length polymerase chain reaction-amplified within a 35-strain field collection, to assess their distribution and allelic diversity. Six T3E repertoire groups were identified, within which 11 representative strains were chosen to challenge the bacterial wilt-resistant eggplants ‘Dingras multiple Purple’ and ‘AG91-25’, and tomato Hawaii7996. The virulence or avirulence phenotypes could not be explained by specific T3E repertoires, but rather by individual T3E genes. We identified seven highly avirulence-associated genes, among which ripP2, primarily referenced as conferring avirulence to Arabidopsis thaliana. Interestingly, no T3E was associated with avirulence to both eggplants. Highly virulence-associated genes were also identified: ripA5_2, ripU, and ripV2. This study should be regarded as a first step toward investigating both avirulence and virulence function of the highlighted genes, but also their evolutionary dynamics in natural R. solanacearum populations.

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The awr Gene Family Encodes a Novel Class of Ralstonia solanacearum Type III Effectors Displaying Virulence and Avirulence Activities

Molecular Plant-Microbe Interactions ◽

10.1094/mpmi-12-11-0321 ◽

2012 ◽

Vol 25 (7) ◽

pp. 941-953 ◽

Cited By ~ 44

Author(s):

Montserrat Solé ◽

Crina Popa ◽

Oriane Mith ◽

Kee Hoon Sohn ◽

Jonathan D. G. Jones ◽

...

Keyword(s):

Gene Family ◽

Pseudomonas Syringae ◽

Ralstonia Solanacearum ◽

Tomato Dc3000 ◽

Type Iii Effectors ◽

Type Iii ◽

New Gene ◽

Transient Overexpression ◽

Effector Recognition

We present here the characterization of a new gene family, awr, found in all sequenced Ralstonia solanacearum strains and in other bacterial pathogens. We demonstrate that the five paralogues in strain GMI1000 encode type III-secreted effectors and that deletion of all awr genes severely impairs its capacity to multiply in natural host plants. Complementation studies show that the AWR (alanine-tryptophan-arginine tryad) effectors display some functional redundancy, although AWR2 is the major contributor to virulence. In contrast, the strain devoid of all awr genes (Δawr1-5) exhibits enhanced pathogenicity on Arabidopsis plants. A gain-of-function approach expressing AWR in Pseudomonas syringae pv. tomato DC3000 proves that this is likely due to effector recognition, because AWR5 and AWR4 restrict growth of this bacterium in Arabidopsis. Transient overexpression of AWR in nonhost tobacco species caused macroscopic cell death to varying extents, which, in the case of AWR5, shows characteristics of a typical hypersensitive response. Our work demonstrates that AWR, which show no similarity to any protein with known function, can specify either virulence or avirulence in the interaction of R. solanacearum with its plant hosts.

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A novel Sec14 phospholipid transfer protein from Nicotiana benthamiana is up-regulated in response to Ralstonia solanacearum infection, pathogen associated molecular patterns and effector molecules and involved in plant immunity

Journal of Plant Physiology ◽

10.1016/j.jplph.2012.04.002 ◽

2012 ◽

Vol 169 (10) ◽

pp. 1017-1022 ◽

Cited By ~ 24

Author(s):

Akinori Kiba ◽

Masahito Nakano ◽

Patrick Vincent-Pope ◽

Hirotaka Takahashi ◽

Tatsuya Sawasaki ◽

...

Keyword(s):

Ralstonia Solanacearum ◽

Nicotiana Benthamiana ◽

Plant Immunity ◽

Phospholipid Transfer Protein ◽

Effector Molecules ◽

Transfer Protein ◽

Phospholipid Transfer ◽

Molecular Patterns

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Faculty Opinions recommendation of Ralstonia solanacearum requires F-box-like domain-containing type III effectors to promote disease on several host plants.

Faculty Opinions – Post-Publication Peer Review of the Biomedical Literature ◽

10.3410/f.1046385.496341 ◽

2006 ◽

Author(s):

Judy Callis

Keyword(s):

Ralstonia Solanacearum ◽

Host Plants ◽

Type Iii Effectors ◽

Type Iii

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The Majority of the Type III Effector Inventory of Pseudomonas syringae pv. tomato DC3000 Can Suppress Plant Immunity

Molecular Plant-Microbe Interactions ◽

10.1094/mpmi-22-9-1069 ◽

2009 ◽

Vol 22 (9) ◽

pp. 1069-1080 ◽

Cited By ~ 147

Author(s):

Ming Guo ◽

Fang Tian ◽

Yashitola Wamboldt ◽

James R. Alfano

Keyword(s):

Pseudomonas Syringae ◽

Plant Immunity ◽

In Planta ◽

Tomato Dc3000 ◽

Type Iii Effector ◽

Type Iii Effectors ◽

Type Iii ◽

Molecular Pattern ◽

Effector Triggered Immunity ◽

Type Iii Protein Secretion

The Pseudomonas syringae type III protein secretion system (T3SS) and the type III effectors it injects into plant cells are required for plant pathogenicity and the ability to elicit a hypersensitive response (HR). The HR is a programmed cell death that is associated with effector-triggered immunity (ETI). A primary function of P. syringae type III effectors appears to be the suppression of ETI and pathogen-associated molecular pattern–triggered immunity (PTI), which is induced by conserved molecules on microorganisms. We reported that seven type III effectors from P. syringae pv. tomato DC3000 were capable of suppressing an HR induced by P. fluorescens(pHIR11) and have now tested 35 DC3000 type III effectors in this assay, finding that the majority of them can suppress the HR induced by HopA1. One newly identified type III effector with particularly strong HR suppression activity was HopS2. We used the pHIR11 derivative pLN1965, which lacks hopA1, in related assays and found that a subset of the type III effectors that suppressed HopA1-induced ETI also suppressed an ETI response induced by AvrRpm1 in Arabidopsis thaliana. A. thaliana plants expressing either HopAO1 or HopF2, two type III effectors that suppressed the HopA1-induced HR, were reduced in the flagellin-induced PTI response as well as PTI induced by other PAMPs and allowed enhanced in planta growth of P. syringae. Collectively, our results suggest that the majority of DC3000 type III effectors can suppress plant immunity. Additionally, the construct pLN1965 will likely be a useful tool in determining whether other type III effectors or effectors from other types of pathogens can suppress either ETI, PTI, or both.

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RNA Sequencing-Associated Study Identifies GmDRR1 as Positively Regulating the Establishment of Symbiosis in Soybean

Molecular Plant-Microbe Interactions ◽

10.1094/mpmi-01-20-0017-r ◽

2020 ◽

Vol 33 (6) ◽

pp. 798-807

Author(s):

Yan Shi ◽

Zhanguo Zhang ◽

Yingnan Wen ◽

Guolong Yu ◽

Jianan Zou ◽

...

Keyword(s):

Rna Sequencing ◽

Plant Immunity ◽

Wild Soybean ◽

Female Parent ◽

Sequencing Analysis ◽

Type Iii Effectors ◽

Type Iii ◽

Soybean Chromosome ◽

Lack Of Information

In soybean (Glycine max)-rhizobium interactions, the type III secretion system (T3SS) of rhizobium plays a key role in regulating host specificity. However, the lack of information on the role of T3SS in signaling networks limits our understanding of symbiosis. Here, we conducted an RNA sequencing analysis of three soybean chromosome segment substituted lines, one female parent and two derived lines with different chromosome-substituted segments of wild soybean and opposite nodulation patterns. By analyzing chromosome-linked differentially expressed genes in the substituted segments and quantitative trait loci (QTL)-assisted selection in the substituted-segment region, genes that may respond to type III effectors to mediate plant immunity–related signaling were identified. To narrow down the number of candidate genes, QTL assistant was used to identify the candidate region consistent with the substituted segments. Furthermore, one candidate gene, GmDRR1, was identified in the substituted segment. To investigate the role of GmDRR1 in symbiosis establishment, GmDRR1-overexpression and RNA interference soybean lines were constructed. The nodule number increased in the former compared with wild-type soybean. Additionally, the T3SS-regulated effectors appeared to interact with the GmDDR1 signaling pathway. This finding will allow the detection of T3SS-regulated effectors involved in legume-rhizobium interactions.

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Isolation of Ralstonia solanacearum hrpB constitutive mutants and secretion analysis of hrpB-regulated gene products that share homology with known type III effectors and enzymes

Microbiology ◽

10.1099/mic.0.28161-0 ◽

2005 ◽

Vol 151 (9) ◽

pp. 2873-2884 ◽

Cited By ~ 21

Author(s):

Naoyuki Tamura ◽

Yukio Murata ◽

Takafumi Mukaihara

Keyword(s):

Pseudomonas Syringae ◽

Ralstonia Solanacearum ◽

Type Iii Secretion ◽

Effector Proteins ◽

Gene Products ◽

Nudix Hydrolase ◽

Type Iii Effectors ◽

Type Iii ◽

Extracellular Secretion ◽

Culture Supernatants

The Hrp type III secretion system (TTSS) is essential for the pathogenicity of the Gram-negative plant pathogen Ralstonia solanacearum. To examine the secretion of type III effector proteins via the Hrp TTSS, a screen was done of mutants constitutively expressing the hrpB gene, which encodes an AraC-type transcriptional activator for the hrp regulon. A mutant was isolated that in an hrp-inducing medium expresses several hrpB-regulated genes 4·9–83-fold higher than the wild-type. R. solanacearum Hrp-secreted outer proteins PopA and PopC were secreted at high levels into the culture supernatants of the hrpB constitutive (hrpB c) mutant. Using hrpB c mutants, the extracellular secretion of several hrpB-regulated (hpx) gene products that share homology with known type III effectors and enzymes was examined. Hpx23, Hpx24 and Hpx25, which are similar in sequence to Pseudomonas syringae pv. tomato effector proteins HopPtoA1, HolPtoR and HopPtoD1, are also secreted via the Hrp TTSS in R. solanacearum. The secretion of two hpx gene products that share homology with known enzymes, glyoxalase I (Hpx19) and Nudix hydrolase (Hpx26), was also examined. Hpx19 is accumulated inside the cell, but interestingly, Hpx26 is secreted outside the cell as an Hrp-secreted outer protein, suggesting that Hpx19 functions intracellularly but Hpx26 is a novel effector protein of R. solanacearum.

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