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Functional assignment to positively selected sites in the core type III effector RipG7 from Ralstonia solanacearum.

ABSTRACT: The soil-borne pathogen Ralstonia solanacearum causes bacterial wilt in a broad range of plants. The main virulence determinants of R.?solanacearum are the type III secretion system (T3SS) and its associated type III effectors (T3Es), translocated into the host cells. Of the conserved T3Es among R.?solanacearum strains, the Fbox protein RipG7 is required for R.?solanacearum pathogenesis on Medicago truncatula. In this work, we describe the natural ripG7 variability existing in the R.?solanacearum species complex. We show that eight representative ripG7 orthologues have different contributions to pathogenicity on M.?truncatula: only ripG7 from Asian or African strains can complement the absence of ripG7 in GMI1000 (Asian reference strain). Nonetheless, RipG7 proteins from American and Indonesian strains can still interact with M.?truncatula?SKP1-like/MSKa protein, essential for the function of RipG7 in virulence. This indicates that the absence of complementation is most likely a result of the variability in the leucine-rich repeat (LRR) domain of RipG7. We identified 11 sites under positive selection in the LRR domains of RipG7. By studying the functional impact of these 11 sites, we show the contribution of five positively selected sites for the function of RipG7CMR15 in M.?truncatula colonization. This work reveals the genetic and functional variation of the essential core T3E RipG7 from R.?solanacearum. This analysis is the first of its kind on an essential disease-controlling T3E, and sheds light on the co-evolutionary arms race between the bacterium and its hosts.

SUBMITTER: Wang K

PROVIDER: S-EPMC6638336 | biostudies-literature | 2016 May

REPOSITORIES: biostudies-literature

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Functional assignment to positively selected sites in the core type III effector RipG7 from Ralstonia solanacearum.

Wang Keke K Remigi Philippe P Anisimova Maria M Lonjon Fabien F Kars Ilona I Kajava Andrey A Li Chien-Hui CH Cheng Chiu-Ping CP Vailleau Fabienne F Genin Stéphane S Peeters Nemo N

Molecular plant pathology 20151202 4

The soil-borne pathogen Ralstonia solanacearum causes bacterial wilt in a broad range of plants. The main virulence determinants of R. solanacearum are the type III secretion system (T3SS) and its associated type III effectors (T3Es), translocated into the host cells. Of the conserved T3Es among R. solanacearum strains, the Fbox protein RipG7 is required for R. solanacearum pathogenesis on Medicago truncatula. In this work, we describe the natural ripG7 variability existing in the R. solanacearu ...[more]

PMID: 26300048

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Project description:The plant pathogen Ralstonia solanacearum possesses two genes encoding a trehalose-6-phosphate synthase (TPS), an enzyme of the trehalose biosynthetic pathway. One of these genes, named ripTPS, was found to encode a protein with an additional N-terminal domain which directs its translocation into host plant cells through the type 3 secretion system. RipTPS is a conserved effector in the R. solanacearum species complex, and homologues were also detected in other bacterial plant pathogens. Functional analysis of RipTPS demonstrated that this type 3 effector synthesizes trehalose-6-phosphate and identified residues essential for this enzymatic activity. Although trehalose-6-phosphate is a key signal molecule in plants that regulates sugar status and carbon assimilation, the disruption of ripTPS did not alter the virulence of R. solanacearum on plants. However, heterologous expression assays showed that this effector specifically elicits a hypersensitive-like response on tobacco that is independent of its enzymatic activity and is triggered by the C-terminal half of the protein. Recognition of this effector by the plant immune system is suggestive of a role during the infectious process.Ralstonia solanacearum, the causal agent of bacterial wilt disease, infects more than two hundred plant species, including economically important crops. The type III secretion system plays a major role in the pathogenicity of this bacterium, and approximately 70 effector proteins have been shown to be translocated into host plant cells. This study provides the first description of a type III effector endowed with a trehalose-6-phosphate synthase enzymatic activity and illustrates a new mechanism by which the bacteria may manipulate the plant metabolism upon infection. In recent years, trehalose-6-phosphate has emerged as an essential signal molecule in plants, connecting plant metabolism and development. The finding that a bacterial pathogen could induce the production of trehalose-6-phosphate in plant cells further highlights the importance of this metabolite in multiple aspects of the molecular physiology of plants.

Dataset Information

Functional assignment to positively selected sites in the core type III effector RipG7 from Ralstonia solanacearum.

Publications

Functional assignment to positively selected sites in the core type III effector RipG7 from Ralstonia solanacearum.

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