Ikeda Ken-ichi, Nakayashiki Hitoshi, Kataoka Tomomori, Tamba Hiroki, Hashimoto Yoko, Tosa Yukio, Mayama Shigeyuki
Labvoratory of Plant Pathology, Kobe University, 1-1 Rokkodaicho, Nada, 657-8501 Kobe, Japan.
Mol Microbiol. 2002 Sep;45(5):1355-64. doi: 10.1046/j.1365-2958.2002.03101.x.
Repeat-induced point mutation (RIP) is a process that detects DNA duplications and peppers their sequences with C:G to T:A transitions in the sexual phase of the life cycle. So far, this unique mechanism has been identified as a currently active process in only two fungal species, Neurospora crassa and Podospora anserina. To determine whether a RIP-like process operates in the plant pathogenic fungus Magnaporthe grisea, the retrotransposon MAGGY and the hygromycin B phosphotransferase gene were introduced into the fungus as multiple transgenes and examined for sequence alterations after a cross. Frequent C:G to T:A transitions in the transgenes were found in the descendants, preferentially in (A/Tp)Cp(A/T)contexts, suggesting that a process similar to RIP functions in M.grisea. We also examined the sequence of another retrotransposon Pyret in six field isolates of M. grisea. Even though no perfect stage has been known in M. grisea under field conditions to date, RIP-like transitions were found in all the field isolates tested. Interestingly, the frequency of the transitions mostly correlated with the fertility of the isolates examined under laboratory conditions. These results imply that the sexual cycle of this fungus exists or existed in the natural field context.
重复诱导点突变（RIP）是一种在生命周期的有性阶段检测DNA重复并在其序列中大量引入C:G到T:A转换的过程。到目前为止，这种独特的机制仅在两种真菌物种，即粗糙脉孢菌和栗疫霉中被确定为当前活跃的过程。为了确定类似RIP的过程是否在植物病原真菌稻瘟病菌中起作用，将反转录转座子MAGGY和潮霉素B磷酸转移酶基因作为多个转基因导入该真菌，并在杂交后检查序列变化。在后代中发现转基因中频繁出现C:G到T:A的转换，优先出现在（A/Tp）Cp（A/T）背景中，这表明类似于RIP的过程在稻瘟病菌中起作用。我们还检查了稻瘟病菌六个田间分离株中另一个反转录转座子Pyret的序列。尽管迄今为止在田间条件下尚未发现稻瘟病菌的有性阶段，但在所测试的所有田间分离株中都发现了类似RIP的转换。有趣的是，转换频率大多与在实验室条件下检测的分离株的育性相关。这些结果表明该真菌的有性循环在自然田间环境中存在或曾经存在。
