An H-NS-like protein involved in the negative regulation of hrp genes in Xanthomonas oryzae pv. oryzae

Abstract

hrp genes encode components of a type III secretion (T3S) system and play crucial roles in the pathogenicity of the rice pathogen Xanthomonas oryzae pv. oryzae (Xoo). A histone-like nucleoid-structuring (H-NS) protein binds DNA and acts as a global transcriptional repressor. Here, we investigated the involvement of an h-ns-like gene, named xrvB, in the expression of hrp genes in Xoo. Under the hrp-inducing culture condition, the expression of a key hrp regulator HrpG increased in the XrvB mutant, followed by activation of the downstream gene expression. Also, in planta, the secretion of a T3S protein (XopR) was activated by the mutation in xrvB. Gel retardation assay indicated that XrvB has DNA-binding activity, but without a preference for the promoter region of hrpG. The results suggest that XrvB negatively regulates hrp gene expression and that an unknown factor(s) mediates the regulation of hrpG expression by XrvB.

GamR, the LysR-Type Galactose Metabolism Regulator, Regulates hrp Gene Expression via Transcriptional Activation of Two Key hrp Regulators, HrpG and HrpX, in Xanthomonas oryzae pv. oryzae

“…In X. oryzae pv. oryzae, three H-NS proteins are encoded in the genome, and at least two of them, XrvA and XrvB, are reported to be involved in hrp gene regulation (24,25). However, XrvA is involved in positive regulation of hrpG expression, which implies that XrvA must negatively regulate an unknown negative regulator of hrpG.…”

“…However, XrvA is involved in positive regulation of hrpG expression, which implies that XrvA must negatively regulate an unknown negative regulator of hrpG. Also, no XrvB binding to the hrpG upstream region has been reported (25). Therefore, GamR might function as an antagonist of the negative regulator(s) for hrpG and hrpX, but the targets could not be H-NS protein(s).…”

“…oryzae possesses three H-NS proteins, and one of them, named XrvA, is involved in the upregulation of hrpG expression (24). However, we previously found that another H-NS protein, XrvB, negatively regulates hrpG expression (25). In addition, the GntR family transcriptional regulator Trh and the two-component signal transduction system PhoP/PhoQ have also been reported to be involved in the transcriptional regulation of hrpG (26,27).…”

H-NS Family Members MvaT and MvaU Regulate the Pseudomonas aeruginosa Type III Secretion System

“…The primary regulator of the E. coli T3SS (Ler) activates transcription by antagonizing H-NS-mediated silencing (57,59). Involvement of H-NS in repression of T3SS gene expression is also seen in Salmonella enterica, Shigella flexneri, and the plant pathogen Xanthomonas oryzae (60)(61)(62).…”

TfmR, a novel TetR‐family transcriptional regulator, modulates the virulence of Xanthomonas citri in response to fatty acids

“…The OmpR family transcriptional regulator HrpG is induced during early infection (Potnis et al ., ) and promotes the expression of the AraC‐type transcriptional activator hrpX , which in turn positively regulates the expression of the T3SS structural components and type III effector genes by binding to a conserved sequence motif (plant‐inducible promoter [PIP]) box) in the promoter regions of these genes (Koebnik et al ., ; Kogenaru et al ., ; Wengelnik and Bonas, ). HrpG and HrpX are subjected to complex regulation through transcription (Kametani‐Ikawa et al ., ; Lu et al ., ), transcript stability (Andrade et al ., ), protein stability (Zhou et al ., ) and post‐transcriptional modification (Li et al ., ), and are under tight metabolic control (Rashid et al ., ; Schulte, ). While many advances have been made in understanding the upstream regulation of HrpG and HrpX, the mechanism that enables the selective induction and activation of these proteins remains unclear.…”