The G-beta subunit MGB1 is involved in regulating multiple steps of infection-related morphogenesis in Magnaporthe grisea.
Trimeric G-proteins transmit extracellular signals to various downstream effectors (e.g. MAP kinases) in eukaryotes. In the rice blast fungus Magnaporthe grisea, the Pmk1 MAP kinase is essential for appressorium formation and infectious growth. The pmk1 deletion mutant fails to form appressoria but still responds to exogenous cAMP for tip deformation. Since gene disruption mutants of three Galpha subunits still form appressoria and are phenotypically different from pmk1 mutants, it is likely that the Pmk1 pathway is activated by Gbeta in M. grisea. In this study, we isolated and characterized the MGB1 gene that encodes the G subunit in M. grisea. Mutants disrupted in MGB1 were reduced in conidiation. Conidia from mgb1 mutants were defective in appressorium formation and failed to penetrate or grow invasively on rice leaves. Exogenous cAMP induced appressorium formation in mgb1 mutants, but these appressoria were abnormal in shape and could not penetrate. The intracellular cAMP level was reduced in mgb1 mutants and the defects in conidiation and hyphal growth were partially suppressed with 1 mM cAMP. Transformants expressing multiple copies of MGB1 were able to form appressoria on hydrophilic surfaces. Our results suggest that MGB1 may be involved in the cAMP signalling for regulating conidiation, surface recognition and appressorium formation. The Pmk1 pathway may be the downstream target of MGB1 for regulating penetration and infectious hyphae growth in M. grisea.
D001483:Base Sequence; D000242:Cyclic AMP / Q000378:metabolism; D004271:DNA, Fungal / Q000737:chemistry / Q000302:isolation & purification; D005656:Fungal Proteins / Q000235:genetics / Q000378:metabolism; D044387:GTP-Binding Protein beta Subunits / Q000235:genetics* / Q000378:metabolism*; D017353:Gene Deletion; D005800:Genes, Fungal; D005816:Genetic Complementation Test; D025301:Hyphae / Q000254:growth & development; D020082:Magnaporthe / Q000166:cytology* / Q000235:genetics* / Q000254:growth & development / Q000472:pathogenicity; D008969:Molecular Sequence Data; D020125:Mutation, Missense; D017853:Phosphotransferases (Alcohol Group Acceptor) / Q000378:metabolism; D010935:Plant Diseases / Q000382:microbiology; D018515:Plant Leaves / Q000382:microbiology; D014774:Virulence / Q000235:genetics
D004271:DNA, Fungal; D005656:Fungal Proteins; D044387:GTP-Binding Protein beta Subunits; D000242:Cyclic AMP; D017853:Phosphotransferases (Alcohol Group Acceptor); C063242:hygromycin-B kinase