Characterization of the GntR family regulator HpaR1 of the crucifer black rot pathogen Xanthomonas campestris pathovar campestris

Abstract

The GntR family transcription regulator HpaR1 identified from Xanthomonas campestris pv. campestris has been previously shown to positively regulate the genes responsible for hypersensitive reaction and pathogenicity and to autorepress its own expression. Here, we demonstrated that HpaR1 is a global regulator that positively regulates diverse biological processes, including xanthan polysaccharide production, extracellular enzyme activity, cell motility and tolerance to various stresses. To investigate the regulatory mechanisms of HpaR1, we began with xanthan polysaccharide production, which is governed by a cluster of gum genes. These are directed by the gumB promoter. Disruption of HpaR1 significantly reduced gumB transcription and an electrophoretic mobility shift assay demonstrated that HpaR1 interacts directly with gumB promoter. DNase I footprint analysis revealed that HpaR1 and RNA polymerase were bound to the sequences extending from −21 to +10 and −41 to +29 relative to the transcription initiation site of gumB, respectively. Furthermore, in vitro transcription assays showed that HpaR1 facilitated the binding of RNA polymerase to gumB promoter, leading to an enhancement of its transcription. These results suggest that HpaR1 regulates gumB transcription via a mechanism similar but different to what was found, until now, to only be used by some MerR family transcription activators.

Xanthomonas campestris sensor kinase HpaS co‐opts the orphan response regulator VemR to form a branched two‐component system that regulates motility

“…EPS and extracellular enzyme assays were performed as previously described (Tang et al, 1991;Su et al, 2016). To estimate EPS production, Xcc strains were spotted onto NYG agar plates supplemented with 2% glucose and grown for 5 days.…”

“…EPS was precipitated from the culture supernatant with ethanol, dried, and weighed. For quantitative measurement of the activity of extracellular enzymes, Xcc strains were cultured in NYG medium, and the activities of protease, endoglucanase (cellulase), and amylase were measured as previously described (Su et al, 2016).…”

Flp, a Fis‐like protein, contributes to the regulation of type III secretion and virulence processes in the phytopathogen Xanthomonas campestris pv. campestris

“…Xanthomonas campestris pv. campestris (Xcc) is one of the best studied of these as it is the causative agent of black rot disease in crucifers, which include many important vegetable brassica crops (Swings and Civerolo, 1993;Vicente and Holub, 2013). Xcc is also an important model for the study of microbe-plant interactions because of its genetic tractability and cultivability.…”

XC_0531 encodes a c-type cytochrome biogenesis protein and is required for pathogenesis in Xanthomonas campestris pv. campestris

“…The diameters of the area occupied by the bacterial cells were measured and these values were used to indicate the motility of the Xcc strains [33]. The experiment was repeated at least three times.…”