The hrpB1 gene of Xanthomonas oryzae pv. oryzicola is required for hypersensitive response in nonhost tobacco and pathogenicity in host rice.

Xanthomonas oryzae pv.oryzicola(Xoc) hrp genes determine the hypersensitive response(HR) in nonhost or resistant host and pathogenicity in host plant.The Hrp products assemble the type Ⅲ secretion system(T3SS) to deliver T3S effectors into rice cell which lead to resistance or susceptibility for pathogen infection.In this study,the hrpB1 gene was mutated by allelic exchange in Xoc.It was found that hrpB1 mutant lost pathogenicity in rice and the ability to excite HR in tobacco.In contrast,the growth of mutant reduced dramatically in leaf tissue of rice.RT-PCR showed that the transcription of hrpB1 was positively regulated by two hrp regulators,HrpG and HrpX.Intriguingly,Western blot illustrated that HrpB1 protein was secreted to the outside of bacteria via T3SS apparatus.These results suggested that hrpB1 was prerequisite for HR induction in tobacco and pathogenicity in rice and may be a novel T3S effector.