XbmR, a novel transcription factor regulates chemotaxis, biofilm formation and virulence in Xanthomonas citri subsp. citri

YARYURA PM; CONFORTE VP; MALAMUD F; ROESCHLIN R; DE PINO V; CASTAGNARO AP; MCCARTHY Y; DOW JM; MARANO MR; VOJNOV AA

Congreso; FEMS 6th congress of european microbiologists; 2015

Citrus canker is one of the most important and aggressive bacterial diseases of citrus trees. The causal agent of this disease is Xanthomonas citri subsp. citri (Xcc). Biofilm formation on citrus leaves plays an important role in epiphytic survival of Xcc. Previous work from our laboratory described a genetic screen for biofilm formation defective mutants in Xcc, this work identified that a mutant with a transposon insertion in XAC3733 (xbmR) had significantly reduced attachment to a polystyrene surface. To gain knowledge about the regulatory mechanisms of Xcc infection For in vitro analysis of biofilm formation, we used confocal laser scanningmicroscopy. For pathogenicity assays grapefruits leaves was used as the host plant for Xcc. Gene expression levels was obtained by qRT-PCR. Intracellular alteration in c-di-GMP was achieved by exogenous expression of either the diguanylate cyclase WspR19 from P. fluorescens or the c-di-GMP phosphodiesterase PA2567 from P.aeruginosa.A knock-out of xbmR led to a substantial downregulation of fliA, which encodes a 28 transcription factor, as well as fliC and XAC0350 which are potential member of the 28 regulon. XAC0350 encodes an HD-GYP domain cyclic di-GMP-phosphodiesterase. These findings suggest that XbmR is a key regulator of flagellar-dependent motility and chemotaxis exerting its action through a regulatory pathway that involves FliA and c-di-GMP.