The small GTPase MoYpt7 is required for membrane fusion in autophagy and pathogenicity of Magnaporthe oryzae

Rab GTPases are required for vesicle-vacuolar fusion during vacuolar biogenesis in fungi. To date, little is known about the biological functions of the Rab small GTPase components in Magnaporthe oryzae. In this study, we investigated MoYpt7 of M.oryzae, a homologue of the small Ras-like GTPase Ypt7 in Saccharomyces cerevisiae. Cellular localization assays showed that MoYpt7 was predominantly localized to vacuolar membranes. Using a targeted gene disruption strategy, a MoYPT7 mutant was generated that exhibited defects in mycelial growth and production of conidia. The conidia of the MoYPT7 mutant were malformed and defective in the formation of appressoria. Consequently, the MoYPT7 mutant failed to cause disease in rice and barley. Furthermore, the MoYPT7 mutant showed impairment in autophagy, breached cell wall integrity, and higher sensitivity to both calcium and heavy metal stress. Transformants constitutively expressing an active MoYPT7 allele (MoYPT7-CA, Gln67Leu) exhibited distinct phenotypes from the MoYPT7 mutant. Expression of MoYPT7-CA in MoYpt7 reduced pathogenicity and produced more appressoria-forming single-septum conidia. These results indicate that MoYPT7 is required for fungal morphogenesis, vacuole fusion, autophagy, stress resistance and pathogenicity in M.oryzae.