Role of DetR in defence is critical for virulence of X anthomonas oryzae pv. oryzae

Summary Like other bacteria, X anthomonas oryzae pv. oryzae ( X oo ), the causal agent of bacterial leaf blight disease in rice, possesses intracellular signalling systems, known as two‐component regulatory systems ( TCSs ), which regulate pathogenesis and biological processes. Completion of the genome sequences of three X oo strains has facilitated the functional study of genes, including those of TCSs , but the biological functions of most X oo   TCSs have not yet been uncovered. To identify TCSs involved in X oo pathogenesis, we generated knockout strains lacking response regulators ( RRs , a cytoplasmic signalling component of the TCS ) and examined the virulence of the RR knockout strains. This study presents a knockout strain ( det R − ) lacking the PXO _04659 gene which shows dramatically reduced virulence relative to the wild‐type. Our studies to elucidate det R function in X oo pathogenesis revealed a reduction in extracellular polysaccharide ( EPS ), intolerance to reactive oxygen species ( ROS ) and deregulation of iron homeostasis in the det R − strain. Moreover, gene expression of regulatory factors, including other RRs and transcription factors ( TFs ), was altered in the absence of DetR protein, as determined by reverse transcription‐polymerase chain reaction ( RT‐PCR ) and/or real‐time quantitative RT‐ PCR analyses. All evidence leads to the conclusion that DetR is essential for X oo virulence through the regulation of the X oo defence system including EPS synthesis, ROS detoxification and iron homeostasis, solely or cooperatively with other regulatory factors.