Sensing and adhesion are adaptive functions in the plant pathogenic xanthomonads

BMC Evolutionary Biology

Armelle Darrasse¹  Nadia Mhedbi-Hajri²  Sandrine Pign³ 

[1] CEA/DSV/IG/Genoscope, 2 rue Gaston Cremieux, Evry Cedex 06, France;UMR077 PaV, INRA, 42, rue Georges Morel, Beaucouz, France;UMR077 PaV, Universit dAngers, 42, rue Georges Morel, Beaucouz, France

关键词: Genetic Lineage;    Adaptive Divergence;    Ralstonia Solanacearum;    Plant Pathogenic Bacterium;    Host Colonisation;   

DOI  :  10.1186/1471-2148-11-67

学科分类：生物科学（综合）

来源: BioMed Central

【 摘 要 】

Bacterial plant pathogens belonging to the Xanthomonas genus are tightly adapted to their host plants and are not known to colonise other environments. The host range of each strain is usually restricted to a few host plant species. Bacterial strains responsible for the same type of symptoms on the same host range cluster in a pathovar. The phyllosphere is a highly stressful environment, but it provides a selective habitat and a source of substrates for these bacteria. Xanthomonads colonise host phylloplane before entering leaf tissues and engaging in an invasive pathogenic phase. Hence, these bacteria are likely to have evolved strategies to adapt to life in this environment. We hypothesised that determinants responsible for bacterial host adaptation are expressed starting from the establishment of chemotactic attraction and adhesion on host tissue. We established the distribution of 70 genes coding sensors and adhesins in a large collection of xanthomonad strains. These 173 strains belong to different pathovars of Xanthomonas spp and display different host ranges. Candidate genes are involved in chemotactic attraction (25 genes), chemical environment sensing (35 genes), and adhesion (10 genes). Our study revealed that candidate gene repertoires comprised core and variable gene suites that likely have distinct roles in host adaptation. Most pathovars were characterized by unique repertoires of candidate genes, highlighting a correspondence between pathovar clustering and repertoires of sensors and adhesins. To further challenge our hypothesis, we tested for molecular signatures of selection on candidate genes extracted from sequenced genomes of strains belonging to different pathovars. We found strong evidence of adaptive divergence acting on most candidate genes. These data provide insight into the potential role played by sensors and adhesins in the adaptation of xanthomonads to their host plants. The correspondence between repertoires of sensor and adhesin genes and pathovars and the rapid evolution of sensors and adhesins shows that, for plant pathogenic xanthomonads, events leading to host specificity may occur as early as chemotactic attraction by host and adhesion to tissues.

【 授权许可】

CC BY