Ketoglutarate Transport Protein KgtP Is Secreted through the Type III Secretion System and Contributes to Virulence in Xanthomonas oryzae pv. oryzae

Abstract

ABSTRACTThe phytopathogenic prokaryoteXanthomonas oryzaepv. oryzae is the causal agent of bacterial leaf blight (BB) of rice and utilizes a type III secretion system (T3SS) to deliver T3SS effectors into rice cells. In this report, we show that the ketoglutarate transport protein (KgtP) is secreted in an HpaB-independent manner through the T3SS ofX. oryzaepv. oryzae PXO99Aand localizes to the host cell membrane for α-ketoglutaric acid export.kgtPcontained an imperfect PIP box (plant-inducible promoter) in the promoter region and was positively regulated by HrpX and HrpG. AkgtPdeletion mutant was impaired in bacterial virulence and growthin planta; furthermore, the mutant showed reduced growth in minimal media containing α-ketoglutaric acid or sodium succinate as the sole carbon source. The reduced virulence and the deficiency in α-ketoglutaric acid utilization by thekgtPmutant were restored to wild-type levels by the presence ofkgtPintrans. The expression ofOsIDH, which is responsible for the synthesis of α-ketoglutaric acid in rice, was enhanced when KgtP was present in the pathogen. To our knowledge, this is the first report demonstrating that KgtP, which is regulated by HrpG and HrpX and secreted by the T3SS inXanthomonas oryzaepv. oryzae, transports α-ketoglutaric acid when the pathogen infects rice.