Inactivation of argG, encoding argininosuccinate synthetase from Xanthomonas oryzae pv. oryzae, is involved in bacterial growth and virulence in planta

Xanthomonas oryzae pv. oryzae (Xoo) is the causal pathogen of bacterial leaf blight disease. To screen components causing blight disease in rice, we mined genes containing a putative plant-inducible promoter (PIP) box in the promoter from a Xoo database and selected 13 genes containing a putative PIP box in their promoter region. Among these genes, we selected argG, encoding putative argininosuccinate synthetase for further study. To study the biological role of argG related to pathogenicity, an insertion mutant of argG was generated using transposon-mediated marker exchange mutagenesis in this pathogen and its spontaneous revertants were generated. This insertion mutant of argG was unable to grow in minimal medium without arginine supplementation and affected the expression of three other genes involved in arginine biosynthesis. This insertion mutant was unable to cause pathogenesis on rice, however, the ability of the pathogen to elicit a hypersensitive response on three nonhost plants was not affected by the mutation. Spontaneous revertants of the mutation completely restored growth in minimal medium and cause pathogenicity in planta. Complementation strain of this mutant by the argG open reading frame partially restored growth in minimal medium and the ability of the pathogen to grow in planta. These results suggest that inactivation of the argG gene causes a metabolic defect that results in impairment of growth and virulence of the pathogen on rice.