Function Of Lipo, PppA Gene Of Acidovorax Oryzae And Mechanisms Of Chitosan Against The Pathogen

Bacterial pathogens are major barriers of rice production in many countries around the world. Acidovorax oryzae is one of the most important seed-borne pathogens, which causes bacterial brown streak (BBS). The six secretion system (T6SS) may be close related to bacterial pathogenicity in A.oryzae. As two important proteins of T6SS in A.oryzae, PppA and Lipo are regulatory protein, which is associated with phosphatase regulation and a peptidoglycan combined protein, which located in the outer membrane, respectively. Upto now, the specific functions of lipo and pppA gene in T6SS are still unknown. The comparison of wild type strain with the two mutants of pppA and lipo constructed in this study revealed that there are no remarkable differences in bacterial motility and extracellular cellulose enzyme activity. For pppA mutant, the biofilm formation and the virulence were significantly alleviated. However, the biofilm formation and pathogenicity were unaffected for lipo mutant. We found that the Lipo protein interacted with the effector Hcp of T6SS, which suggests they may play a key role in plant pathogenicity together.In this study, we also found that chitosan could inhibit the cell growth and biofilm formation of A. oryzae. Results indicated that chitosan solutions at0.10,0.20, and0.40mg/ml inhibited the in vitro growth of A. oryzae, and in general the inhibitory efficiency increased with the increase of both chitosan concentration and the incubation time.Besides, the results of membrane integrity test and transmission electron microscopic showed that chitosan played an important role in the destruction of the cell membrane and may induce the membrane dissolution. In addition, the genes expressions of secretion systems were also affected by chitosan. It suggests that all these interations on the membrane may inhibit growth of the pathogen.