hpaR, a PutativemarRFamily Transcriptional Regulator, Is Positively Controlled by HrpG and HrpX and Involved in the Pathogenesis, Hypersensitive Response, and Extracellular Protease Production ofXanthomonas campestrisPathovar campestris

Abstract

The MarR family of transcriptional regulators of bacteria are involved in the regulation of many cellular processes, including pathogenesis. In this work, we have demonstrated genetically that hpaR (hpa, hrp associated), which encodes a putative MarR family regulator, is involved in the hypersensitive response (HR), pathogenicity, and extracellular protease production of the phytopathogenic bacterium Xanthomonas campestris pathovar campestris. A mutation in hpaR resulted in complete loss of virulence in the host plant cabbage, a delayed and weakened HR in the nonhost plant pepper ECW-10R, and an increase in extracellular protease production. Detection of the ␤-glucuronidase activity of a plasmid-driven hpaR promoter-gusA reporter revealed that the expression of hpaR is positively controlled by HrpG and HrpX and is suppressed in rich medium while being strongly induced in minimal and hrp-inducing media and inside the host. These findings indicate that hpaR belongs to the hrpG and hrpX regulon and that HrpX regulates the extracellular protease production via hpaR in X. campestris pv. campestris.

SlyA, a MarR Family Transcriptional Regulator, Is Essential for Virulence inDickeya dadantii3937

“…carotovora) (58), and hpaR in Xanthomonas campestris pv. campestris (62). It has been demonstrated that the role of MarR in controlling the expression of virulence-associated genes varies among pathogens (7,22,27,29,30,34,44,45,62).…”

Elucidation of the Regulon and cis -Acting Regulatory Element of HrpB, the AraC-Type Regulator of a Plant Pathogen-Like Type III Secretion System in Burkholderia pseudomallei

“…However, HpaR, a transcriptional regulator that is positively regulated by HrpX in Xanthomonas campestris pv. campestris, is required for pathogenicity but does not regulate any T3SS genes (72). While there is no ortholog of HpaR in B. pseudomallei, our analysis did indicate that a two-component regulatory system, a LuxR family regulator, and two AraC-type regulators may be downstream components of a HrpB bp regulatory cascade.…”

Secretion, modification, and regulation of Ax21

“…The T3SS secretes proteins directly into host cells. HrpX also controls expression of type III effectors (T3E), which are secreted proteins via the T3SS [51,52]. We have shown that expression of hrpA and hrpX in Xoo is significantly higher in the presence of low Ca 2+ concentrations in the wild-type strain, but not in the PXO99DphoP strain [33].…”