Molecular Plant Pathology (2019) 20, 33-50

Valérian Meline, Wesley Delage, Chrystelle Brin, Camille Li-Marchetti, Daniel Sochard, Matthieu Arlat, Céline Rousseau, Armelle Darrasse, Martial Briand, Guillaume Lebreton, Perrine Portier, Marion Fischer-Le Saux, Karine Durand, Marie-Agnès Jacques, Etienne Belin and Tristan Boureau (2019)
Role of the acquisition of a type 3 secretion system in the emergence of novel pathogenic strains of Xanthomonas
Molecular Plant Pathology 20 (1), 33-50
Abstract: 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.
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Link to article at publishers website
Database assignments for author(s): Tristan Boureau, Matthieu Arlat, Marion Fischer-Le Saux, Marie-Agnès Jacques, Tristan Boureau, Perrine Portier

Research topic(s) for pests/diseases/weeds:
molecular biology - genes

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Pest and/or beneficial records:

Beneficial	Pest/Disease/Weed	Crop/Product	Country	Quarant.
	Xanthomonas campestris pv. campestris