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

AVR-Pita是一个与稻瘟病菌抗性基因Pita对应的无毒基因。该基因的同源物不仅存在于Oryza分离株中，也存在于Setaria分离株、Panicum分离株、Digitazia分离株等中。我们克隆了这些同源物及其侧翼区域。从Cenchrus分离的同源物两侧没有任何已知的转座因子。另一方面，来自Digitaria分离株的基因位于反转录转座子Inago 1的两个拷贝之间。千年Panicum milium和狗尾草（Setaria viridis）分离株的分离株两侧是Inago 1的副本。水稻和意大利稻分离株中存在多个反转录转座子的单独LTR拷贝。当用这些同源物的DNA序列构建树形图时，Cenchrus分离物的同源物位于其他同源物的根部，而Oryza分离物的同源物位于远端位置。为了研究这些同源物的功能，我们将它们引入到对有皮塔病的水稻品种Yashiromochi有毒的Oryza Slate病毒P2-b中。这些转化子的感染实验表明，来自Digitazia、Panicurn和Setaria Slates的同源物保持了它们作为无毒基因的功能。我们认为这是因为这些同源物没有机会与Pita相互作用。

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.