StoS and SreKRS iTRAQ profiling

Xanthomonas oryzae pv. oryzae (Xoo) is a notorious rice pathogen that causes the destructive rice disease bacterial blight. Two-component signal transduction systems (TCSs) are widely used by bacteria to sense and adapt to the environment. However, the profound mechanism how the TCSs execute the environmental adaption remains elusive. In this study, genome-wide TCSs gene knockout in Xoo PXO99A found that StoS (stress tolerance-related oxygen sensor) and SreKRS (salt response kinase, regulator, and sensor) positively regulate EPS production and swarming. Surprisingly, the compromise of two important virulence traits and stress resistance did not attenuate the virulence. To better understand intrinsic function of StoS and SreKRS, quantitative proteomic isobaric tags for relative and absolute quantitation (iTRAQ) was employed. iTRAQ data indicated that carbohydrate metabolisms proteins and chemotaxis proteins, which could be responsible for the EPS and swarming regulation, respectively, were down-regulated in stoS and sreK mutants. Consistent with stoS and sreK mutants exhibiting similar phenotype, the signaling circuits of StoS and SreKRS were found to overlap each other. Moreover, StoS and SreKRS were revealed to moderate expression of the major virulence factor, hypersensitive response and pathogenicity (Hrp) proteins by HrpG-HrpX circuit. Most important, we found that the Xoo strain equipped with StoS and SreKRS outcompete the strain without StoS or SreKRS co-infecting rice and growing outside host. Our findings imply the two TCSs, StoS and SreKRS, could confer environmental fitness on Xoo. Therefore, here we proposed that StoS and SreKRS adopt a novel strategy by moderating Hrp protein expression together with promoting the EPS and motility to adapt to environment.