Identification à l'échelle génomique des effecteurs dépendant du système de sécrétion de type III de la bactérie phytopathogène Ralstonia solanacearum

TOULOUSE3-BU Sciences (315552104) / SudocSudocFranceF

Pseudomonas syringae type III effector repertoires : last words in endless arguments

Many plant pathogens subvert host immunity by injecting compositionally diverse but functionally similar repertoires of cytoplasmic effector proteins. The bacterial pathogen Pseudomonas syringae is a model for exploring the functional structure of such repertoires. The pangenome of P. syringae encodes 57 families of effectors injected by the type Ill secretion system. Distribution of effector genes among phylogenetically diverse strains reveals a small set of core effectors targeting antimicrobial vesicle trafficking and a much larger set of variable effectors targeting kinase-based recognition processes. Complete disassembly of the 28-effector repertoire of a model strain and reassembly of a minimal functional repertoire reveals the importance of simultaneously attacking both processes. These observations, coupled with growing knowledge of effector targets in plants, support a model for coevolving molecular dialogs between effector repertoires and plant immune systems that emphasizes mutually-driven expansion of the components governing recognition

Characterization of the cis-Acting Regulatory Element Controlling HrpB-Mediated Activation of the Type III Secretion System and Effector Genes in Ralstonia solanacearum

The ability of Ralstonia solanacearum to cause disease on plants depends on its type III secretion system (TTSS) encoded by hrp genes. The expression of hrp genes and known TTSS substrates is coordinately regulated by HrpB, a member of the AraC family of transcriptional regulators. Two HrpB-regulated promoters (hrpY and popABC) were characterized by deletion analysis, and the HrpB-dependent activation of these promoters was found to be conferred by a 25-nucleotide DNA element, the hrp(II) box (TTCGn16TTCG), which is present in other hrp promoters. The hrp(II) box element is an imperfect plant inducible promoter box, an element which was originally found in hrp promoters of Xanthomonas campestris (S. Fenselau and U. Bonas, Mol. Plant-Microbe Interact. 8:845-854, 1995) but which was not characterized at the molecular level. Site-directed mutagenesis showed that the hrp(II) box is essential for hrpY promoter activation in vivo. Functional analysis of the hrp(II) box element identified critical parameters that are required for HrpB-dependent activity. Further mapping analyses of several other hrpB-dependent promoters also indicated that the position of the hrp(II) box is conserved, at −70 to −47 bp from the transcriptional start. As a first step toward identifying novel TTSS effectors, we used the hrp(II) box consensus sequence to search for potential HrpB-regulated promoters in the complete genome sequence of R. solanacearum strain GMI1000. Among the 114 genes identified, a subset of promoters was found to have a structural relationship with hrp promoters, thus providing a pool of candidate genes encoding TTSS effectors

The Complete Genome Resource of Xanthomonas oryzae pv. oryzae CIX2779 Includes the First Sequence of a Plasmid for an African Representative of This Rice Pathogen

The bacterial plant pathogen Xanthomonas oryzae pv. oryzae is responsible for the foliar rice bacterial blight disease. Genetically contrasted, continent-specific, sublineages of this species can cause important damages to rice production both in Asia and Africa. We report on the genome of the CIX2779 strain of this pathogen, previously named NAI1 and originating from Niger. Oxford Nanopore long reads assembly and Illumina short reads polishing produced a genome sequence composed of a 4,725,792-bp circular chromosome and a 39,798-bp-long circular plasmid designated pCIX2779_1. The chromosome structure and base-level sequence are highly related to reference strains of African X. oryzae pv. oryzae and encode identical transcription activator-like effectors for virulence. Importantly, our in silico analysis strongly indicates that pCIX2779_1 is a genuine conjugative plasmid, the first indigenous one sequenced from an African strain of the X. oryzae species. [Graphic: see text] Copyright © 2022 The Author(s). This is an open access article distributed under the CC BY 4.0 International license

Inventory and functional analysis of the large Hrp regulon in Ralstonia solanacearum: identification of novel effector proteins translocated to plant host cells through the type III secretion system

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Salt distribution in the Senegal middle valley. Analysis of a saline structure on the future irrigation schemes from N'Galenka creek.

International audienceIn the middle Senegal valley, the saline soil distribution is not related to the present faint topography. This lack of logic is one of the major constraints for establishment of new irrigated schemes. The salt distribution is here studied to better understand its variability, and to describe its structure and spatial arrangement. Saline areas are delineated by measuring the electromagnetic soil conductivity (ECm), a rapid technique with a portable instrument (EM38). The results indicate that the saline soils are distributed as stripes. A detailed examination revealed that this major stripe is actually composed of two parallel minor stripes, and the comparison with the aerial photograph shows that one lies in a former creek bed, and the other is fringing it on the southern bank. The stripe is intersected by an actual creek bed, indicating that the salt distribution is ancient, related to the former geomorphology, and does not result from a recent remobilisation of the marine salt deposits incorporated in the soil. The identification of this relationship between the present saline soil distribution and the former geomorphology allows us to survey the whole N'Galenka region (about 6000 ha) using the ECm measurements on selected transects