Genome sequence of Xanthomonas oryzae pv. oryzae suggests contribution of large numbers of effector genes and insertion sequences to its race diversity

The plant-pathogenic prokaryote Xanthomonas oryzae pv. oryzae (Xoo) causes bacterial blight, one of the most important diseases of rice. The bacterium is a model organism for the analysis of plant-pathogen interaction, because more than 30 races differing in virulence and 25 resistance genes in rice have been reported to date. We present here the complete genome sequence of Xoo strain MAFF 31101 S. The size of the genome was 4,940,217 bp, in a single circular chromosome. The genome structure of Xoo MAFF 311018 was characterized by large numbers of effector (avr) genes of the avrBs3/pth family and insertion sequences (ISs). RFLP analysis of diverse strains using ISXol as a probe suggests that the prevalence of mobile elements in this species, which can bring about genome inversions and rearrangement, may have played a major role in generating the high degree of genetic diversity and race differentiation characteristic of this pathogen. The Xoo MAFF 311018 sequence was also highly similar to those of X. axonopodis pv. citri and X. campestris pv. campestris with the exception of the large number of effectors and IS elements, and numerous inversions and rearrangements.