Abstract:

【Objective】 Repertoires of pathogenicity effectors in Xanthomonas oryzae pv. oryzicola are injected into plant cells through type-Ⅲ secretion system (T3SS) which is encoded by the hrp (hypersensitive response and pathogenicity) genes, but it is unclear what roles the hrcJ gene plays in pathogen pathogenesis in rice and in T3SS formation. 【Method】 In this report, the hrcJ gene was knocked out by marker exchange method. 【Result】 It was found that the mutant had lost the ability to trigger HR in tobacco and pathogenicity in rice. Protein-protein interactions, revealed by yeast two-hybrid system, demonstrated that the lipoprotein domain at N-terminal of HrcJ interacted with HrcC and the transmembrane domain at C-terminal interacted with HrcV, indicating that HrcJ was a linker protein between the inner and out membranes of the pathogen cell for T3SS formation. Complementation assays in planta showed that either the deletion in the lipoprotein domain or in the transmembrane domain did not restore HR induction in tobacco and pathogenicity in rice to the hrcJ mutant. The reverse transcriptional polymerase chain reaction (RT-PCR) revealed that the hrcJ gene expression was regulated by the hrpX gene and the expression of the effector gene hpa1 was not affected in the hrcJ mutant. 【Conclusion】 These results suggest that the hrcJ gene is required not only for HR induction in tobacco and pathogenicity in rice, but also in T3SS formation through which pathogenicity determinants are secreted into plant cells.

Key words: Xanthomonas oryzae pv.oryzicola, hrcJ, type-Ⅲ secretion system, pathogenicity, hypersensitive response