Genome-wide identification of fitness determinants in theXanthomonas campestrisbacterial pathogen during early stages of plant infection

Abstract

AbstractPlant diseases are an important threat to food production. While major pathogenicity determinants required for disease have been extensively studied, less is known on how pathogens thrive during host colonization especially at early infection stages. Here, we used randomly barcoded-transposon insertion site sequencing (RB-TnSeq) to perform a genome-wide screen and identify key bacterial fitness determinants of the vascular pathogenXanthomonas campestrispv.campestris(Xcc) during infection of the cauliflower host plant (Brassica oleracea). This high-throughput analysis was conducted in hydathodes, the natural entry site ofXcc, in xylem sap and in synthetic media.Xccdid not face a strong bottleneck during hydathode infection. 183 genes important for fitness were identified in plant-associated environments with functional enrichment in genes involved in metabolism when only few genes known to be involved in virulence were found to be affected. The biological relevance of 13 genes was independently confirmed by phenotyping single mutants. Notably, we show that the XC_3388, a protein with no known function (DUF1631), plays a key role in the adaptation and virulence ofXccpossibly through c-di-GMP-mediated regulation. This study thus revealed yet unsuspected social behaviors adopted byXccindividuals when confined inside hydathodes at early infection stages.