Repeat-Induced Point Mutation (RIP) in Magnaporthe Grisea: Evidence for the Presence of Sexual Cycle in Nature

Abstract

The RIP (repeat-induced point mutation) process introduces C:G to T:A transitions into duplicated sequences during a specific period in the sexual reproduction and has been reported in only two fungal species, Neurospora crassa and Podospora anserina. To investigate whether a RIP-like process operates in 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 asexual growth and sexual crossing. Numerous C:G to T:A transitions were found in the transgenes, preferentially in (A/Tp)Cp(A/T) contexts, in the sexual progenies, suggesting that a RIP-like process functions in M. grisea. We also examined the sequence of another retrotransposon, Pyret, in field isolates of M. grisea. Even though the perfect stage rarely has been observed in M. grisea under field conditions, RIP-like transitions were found in all the field isolates tested and were correlated with the fertility of the isolates in Petri dishes. Analysis of RIP-like transitions in repetitive sequences may provide a tool to estimate the frequency of sexual recombination of M. grisea isolates.