Diversification and transposition of avirulence genes in Magnaporthe oryzae prompted by the instability of subtelomeres

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AVR-Pita is an avirulence gene corresponding-to Pita, a rice gene for resistance to the rice blast fungus, Magnaporthe oryzae. Homologues of this gene are present not only in Oryza isolates, but also in Setaria isolates, Panicum isolates, Digitazia isolates, etc. We cloned these homologues with their flanking regions. A homologue from a Cenchrus isolate was not flanked by any known transposable elements. On the other hand, those from Digitaria isolates were located between two copies of a retrotransposon, Inago 1. Those from Panicum miliaceum and Setaria viridis isolates were flanked by a copy of Inago 1. Those from Oryza sativa and Setana italica isolates were accompanied by several copies of solo LTR of retrotransposons. When a dendrogram was constructed from the DNA sequences of these homologues, the homologue from the Cenchrus isolate was located at the root of the others, while those from Oryza isolates were located at a distal position.To examine the function of these homologues, they were introduced into P2-b, an Oryza Slate virulent on rice cultivar Yashiromochi with Pita. Infection assays with these transformants revealed that the homologues from Digitazia, Panicurn and Setaria Slates maintained their function as avirulence genes. We suggest that this is because these homologues have not had a chance to interact with Pita.