Thesis defense

Céline Rousseau : "Consequences of host adaptation on evolution of type III effectors repertoires in Xanthomonas-related bacteria" - March, 28th

Soutenance de thèse, UMR IRHS (Inra, Agrocampus Ouest, Université d'Angers), centre Inra Angers-Nantes © Nathalie Mansion
Updated on 04/14/2014
Published on 03/06/2014

Céline ROUSSEAU

Abstract
The genus Xanthomonas comprises 27 plant-associated bacterial species, some of them being pathogenic. Host specialization is very high for bacteria belonging to Xanthomonas genus. In each Xanthomonas species, numerous pathovars were defined. A pathovar is a subspecific division grouping all bacterial strains that cause the same symptom type on the same plant-host range. Overall the virulence factors of the Xanthomonas, type III effectors (T3Es) have a dual role. They promote virulence on susceptible hosts, whereas they trigger specific defenses in resistant plants. T3Es repertoires vary among Xanthomonas strains. Previously, a correlation between T3Es repertoires and species subdivision in pathovars were shown. The goal of this study was to enlight evolutive mecanisms that have led to T3Es repertoires modification and to the potential modification of the host range of Xanthomonas.
A first approach, based on the comparison of genomic sequences of 21 stains belonging to various species of Xanthomonas, allowed the identification of gains and losses of T3Es genes that led to the variability observed in the T3Es repertoires. Many T3Es that have a potential role in host adaptation were identified. A second approach based on the nucleotidic sequences analysis of twelve T3Es genes was taken on a large X. axonopodis strains collection. This approach allowed the identification of selective pressures leading to a potential modification of pathogenicity. This work formulated numerous functional hypotheses. In order to test them, a high-throughput phenotyping method, based on chlorophyll fluorescence image analysis, was established.
Keywords: host adaptation, selective pressures, type III effector repertoires, Xanthomonas, phenotyping