The gpsX gene encoding a glycosyltransferase is important for polysaccharide production and required for full virulence in Xanthomonas citri subsp. citri

Abstract

BackgroundThe Gram-negative bacterium Xanthomonas citri subsp. citri (Xac) causes citrus canker, one of the most destructive diseases of citrus worldwide. In our previous work, a transposon mutant of Xac strain 306 with an insertion in the XAC3110 locus was isolated in a screening that aimed at identifying genes related to biofilm formation. The XAC3110 locus was named as bdp24 for biofilm-defective phenotype and the mutant was observed to be affected in extracellular polysaccharide (EPS) and lipopolysaccharide (LPS) biosynthesis and cell motility. In this study, we further characterized the bdp24 (XAC3110) gene (designated as gpsX) using genetic complementation assays and expanded the knowledge about the function of the gpsX gene in Xac pathogenesis by investigating the roles of gpsX in EPS and LPS production, cell motility, biofilm formation on host leaves, stress tolerance, growth in planta, and host virulence of the citrus canker bacterium.ResultsThe gpsX gene encodes a putative glycosyltransferase, which is highly conserved in the sequenced strains of Xanthomonas. Mutation of gpsX resulted in a significant reduction of the amount of EPS and loss of two LPS bands visualized on sodium dodecylsulphate- polyacrylamide gels. Biofilm assays revealed that the gpsX mutation affected biofilm formation by Xac on abiotic and biotic surfaces. The gpsX mutant showed delayed bacterial growth and caused reduced development of disease symptoms in susceptible citrus leaves. The gpsX mutant was more sensitive than the wild-type strain to various stresses, including the H2O2 oxidative stress. The mutant also showed attenuated ability in cell motility but not in flagellar formation. Quantitative reverse transcription-PCR assays indicated that mutation of gpsX did not affect the expression of virulence genes such as pthA in Xac strain 306. The affected phenotypes of the gpsX mutant could be complemented to wild-type levels by the intact gpsX gene.ConclusionsTaken together, our data confirm that the gpsX gene is involved in EPS and LPS synthesis and biofilm formation in Xac and suggest that the gpsX gene contributes to the adaptation of Xac to the host microenvironments at early stage of infection and thus is required for full virulence on host plants.

Genetic and Molecular Basis of Kingella kingae Encapsulation

“…A glycosyltransferase required for encapsulation in Xanthomonas citri subsp. citri is encoded by the gpsX gene, which is also outside the locus with the other capsule biosynthesis genes (31). These examples highlight that capsule synthesis genes may reside in distinct regions of the chromosome and underscore the importance of understanding how the K. kingae capsule genes are coordinately regulated.…”

WxcX is involved in bacterial attachment and virulence in Xanthomonas campestris pv. campestris

“…vesicatoria wxcB , X. citri subsp. citri gpsX , nlxA , and wxacO , and Xcc galU and xagB , play a role in environmental stress tolerance. All of these genes are also important for lipopolysaccharide synthesis except for wxcB .…”

Bacteria from the citrus phylloplane can disrupt cell–cell signalling in Xanthomonas citri and reduce citrus canker disease severity

“…The infiltrated leaves were photographed 21 days post‐inoculation (DPI). To resemble natural infection of citrus canker, the infections were also performed by a spray method as described by Li & Wang (), with modifications. Briefly, the abaxial surfaces of fully expanded, immature leaves of each plant were sprayed with a mix solution of each DSF inhibitory bacteria and Xcc 306 at a final concentration of 10 7 CFU mL −1 in 10 m m MgCl 2 for each strain.…”