Open AccessRole of the acquisition of a type 3 secretion system in the emergence of novel pathogenic strains of Xanthomonas
Author(s) -
Meline Valérian,
Delage Wesley,
Brin Chrystelle,
LiMarchetti Camille,
Sochard Daniel,
Arlat Matthieu,
Rousseau Céline,
Darrasse Armelle,
Briand Martial,
Lebreton Guillaume,
Portier Perrine,
FischerLe Saux Marion,
Durand Karine,
Jacques MarieAgnès,
Belin Etienne,
Boureau Tristan
Publication year - 2019
Publication title -
molecular plant pathology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.945
H-Index - 103
eISSN - 1364-3703
pISSN - 1464-6722
DOI - 10.1111/mpp.12737
Subject(s) - biology , effector , virulence , xanthomonas , type three secretion system , microbiology and biotechnology , gene , plasmid , secretion , nicotiana benthamiana , horizontal gene transfer , population , pathogenic bacteria , genetics , genome , bacteria , biochemistry , demography , sociology
Summary Cases of emergence of novel plant‐pathogenic strains are regularly reported that reduce the yields of crops and trees. However, the molecular mechanisms underlying such emergence are still poorly understood. The acquisition by environmental non‐pathogenic strains of novel virulence genes by horizontal gene transfer has been suggested as a driver for the emergence of novel pathogenic strains. In this study, we tested such an hypothesis by transferring a plasmid encoding the type 3 secretion system (T3SS) and four associated type 3 secreted proteins (T3SPs) to the non‐pathogenic strains of Xanthomonas CFBP 7698 and CFBP 7700, which lack genes encoding T3SS and any previously known T3SPs. The resulting strains were phenotyped on Nicotiana benthamiana using chlorophyll fluorescence imaging and image analysis. Wild‐type, non‐pathogenic strains induced a hypersensitive response (HR)‐like necrosis, whereas strains complemented with T3SS and T3SPs suppressed this response. Such suppression depends on a functional T3SS. Amongst the T3SPs encoded on the plasmid, Hpa2, Hpa1 and, to a lesser extent, XopF1 collectively participate in suppression. Monitoring of the population sizes in planta showed that the sole acquisition of a functional T3SS by non‐pathogenic strains impairs growth inside leaf tissues. These results provide functional evidence that the acquisition via horizontal gene transfer of a T3SS and four T3SPs by environmental non‐pathogenic strains is not sufficient to make strains pathogenic. In the absence of a canonical effector, the sole acquisition of a T3SS seems to be counter‐selective, and further acquisition of type 3 effectors is probably needed to allow the emergence of novel pathogenic strains.