Molecular analysis of species-specific parasitism in Magnaporthe grisea

对稻瘟病菌种特异性寄生的机理进行了研究。由狗尾草分离物与三粒小麦分离物杂交产生的F_1群体对小麦的致病力表现出双因素分离。这些基因被命名为pwt1和pwt2。以燕麦和普通小麦为父本的杂交F1群体在燕麦上表现单因素分离。该基因被命名为Pat1。在批量分离分析中发现了紧密连锁的AFLP标记。染色体行走正在进行这些基因的克隆。从马唐分离株中提取了一种植物毒素。在各种禾本科植物中，马唐对该毒素的敏感性最高。只有马唐菌株才能大量产生吡喃菌素H，突变株丧失了对马唐的致病性。经吡沙拉菌素H处理的马唐叶片可被非病原菌侵染。这些结果表明，稻瘟病菌H是马唐分离株种属特异性寄生的决定因素，反转录转座子Maggy是已发现的稻瘟病菌基因组中最活跃的转座元件。在水稻和狗尾草分离物中存在Maggy，而在其他分离物中不存在Maggy。我们推测，该元件可能参与了这些分离物的小种专一性的进化。

Mechanisms of the species-specific parasitism in Magnaporthe grisea were investigated. An F1 population derived from a cross, a Setaria isolate x a Tritucum isolates, showed bifactorial segregation in the pathogenicity on wheat. These genes were designated as Pwt1 and Pwt2. Another F1 population derived from a cross, an Avena isolate and a Triticum isolate, showed monofactorial segregation on oat. This gene was designated as Pat1. Closely linked AFLP markers were found in bulked segregant analyses. Chromosome walking is under way toward cloning of those genes.A phytotoxin was extracted from a Digitaria isolate. The toxin was revealed to be Pyrichalasin H.Among various gramineous plants, crabgrass (the host of Digtaria isolates) showed the highest susceptibility to this toxin. Pyrichalasin H was produced in a large quantity only by Digitaria isolates, and Pyrichalasin H-defidient mutants lost their pathogenicity on crabgrass. Crabgrass leaves treated with Pyrichalasin H became accessible to nonpathogens. These results suggested that Pyrichalasis H is a determinant of the species-specific parasitism of Digitaria isolates.Retrotransposon MAGGY was the most active element among transposable elements that have been found in the genome of Magnaporthe grisea. MAGGY was present in Oryza isolates and Setaria isolates, but absent in other isolates. We assuned that this element may have been involved in the evolution of the race- cultivar specificity in those isolates.