Type Ⅲ secretion effector gene hpaF is required for full virulence of Xanthomonas oryzae pv. oryzae

Objective Xanthomonas oryzae pv. oryzae (Xoo) is the causal agent of rice bacterial leaf blight disease. The type Ⅲ secretion system (T3SS) and type Ⅲ secretion effectors (T3SEs) play important roles in the pathogenesis of this phytopathogen. The gene PXO_03420 of Philippines strain Xoo PXO99^A is annotated as hpaF gene, which was predicted to encode T3SE gene with leucine-rich repeat domains. The purpose of the study is to identify the function of gene PXO_03420(hpaF), which can provide theoretical supports for the study of type Ⅲ secretion effectors of Xoo.

Method The hpaF gene deletion mutant was constructed by homologous double exchange mutational method. The mutant was subjected to phenotypic analysis, virulence assays and genetic complementation experiments.

Result and conclusion  It was found that the virulence of hpaF gene mutant on rice, Oryza sativa L. japonica cv. Nipponbare, was reduced by 51.81% compared with the wild type strain, and the hypersensitive response (HR) induction of the mutant on the leaves of non-host castor oil plant, Ricinus communis, was significantly weakened. The intact coding region of hpaF carried by pLAFR3 could partly complement the virulence of mutant to the level of wild type strain. This study demonstrates that hpaF gene is required for full virulence of Xoo.