A Gγ subunit promoter T-DNA insertion mutant—A1-412 of Magnaporthe grisea is defective in appressorium formation, penetration and pathogenicity

Abstract

In our previous studies, a nonpathogenic mutant of Magnaporthe grisea, A1-412, which was defective in appressorium formation, penetration and infectious growth, was obtained by T-DNA insertional mutagenesis. Here we reported the identification and characterization of the corresponding gene. Sequence analysis of the genomic DNA franking T-DNA isolated by TAIL-PCR technique showed that T-DNA was inserted into the promoter region of the predicted G protein γ-subunit gene MGG1 (for Magnaporthe grisea G protein Gamma subunit). MGG1 is predicted to encode a 93-aa protein with a typical G-protein gamma like domain (GGL) and C-terminal CAAX box. The amino-acid sequence of MGG1 is highly identical to the Gγ subunits of other filamentous fungi. Further phenotypic investigation of A1-412 showed that exogenous cAMP could induce appressorium formation, although the formed appressoria were abnormal in shape and unable to penetrate onion epidemis or rice leaves. Moreover, few perithecia were observed when A1-412 was crossed with the appropriate mating-type strain. The above phenotypes in A1-412 were partially complemented by reintroduction of the gene MGG1. Our results indicate that the G-protein gamma subunit MGG1 may be involved in regulating morphogenesis, mating and pathogenicity in M. grisea.