Analysis of Virulence and Growth of a Purine Auxotrophic Mutant of Xanthomonas Oryzae Pathovar Oryzae

Xanthomonas oryzae pv. oryzae (Xoo) causes bacterial blight of rice. A random insertional mutant library of Xoo KACC10331 was constructed using a Tn5-derived transposon, and the virulence of the mutants against the susceptible rice cultivar IR24 was assayed. After the virulence assay, the M793 (purD::Tn5) mutant that had reduced virulence against the rice plants was isolated. Thermal asymmetric interlaced-PCR and sequence analysis revealed that the transposon was inserted into the purD gene (encodes a phosphoribosylamine-glycine ligase) of the M793 mutant. The reverse transcriptase-PCR assay revealed that the mutation of the purD gene did not affect the expression of other purine biosynthesis genes. However, the M793 mutant required exogenous purines and thiamine for growth in minimal media. These results indicate that the purD gene plays a crucial role in the growth and virulence of Xoo.