Molecular basis for loss of virulence in strain AM16.

The rapid virulence variation of () to rice is a big challenge for rice blast control. Even though many studies have been done by scientists all over the world, the mechanism of virulence variation in remains elusive. AM16, an avirulent strain reported in our previous study, provides an excellent entry point to explore the mechanism of virulence variation in . In this study, we found that the and had specific mutations in strain AM16. The AM16 strains overexpressing or (and) allele from strain Guy11 displayed significantly increasing conidiation, functional appressorium formation, and restoring pathogenicity to rice. Moreover, we observed that the strains overexpressing had stronger conidia forming capacity than that of the strains overexpressing , while the appressorium formation rate of strains overexpressing was similar to that of strains overexpressing - , much higher than that of the strains overexpressing . Taken together, our results reveal that the natural mutation of and genes are important, but not the sole cause, for the loss of virulence in strain AM16. The functional difference between Pmk1 and Mac1 in the growth and development of was first discovered, providing new insight into the pathogenic mechanism of .