G Protein α Subunit Genes Control Growth, Development, and Pathogenicity of Magnaporthe grisea

Three G protein alpha subunit genes have been cloned and characterized from Magnaporthe grisea: magA is very similar to CPG-2 of Cryphonectria parasitica; magB is virtually identical to CPG-1 of Cryphonectria parasitica, to gna1 of Neurospora crassa, and to fadA of Emericella nidulans; and magC is most similar to gna2 of Neurospora crassa. Homologous recombination resulting in targeted deletion of magA had no effect on vegetative growth, conidiation, or appressorium formation. Deletion of magC reduced conidiation, but did not affect vegetative growth or appressorium formation. However, disruption of magB significantly reduced vegetative growth, conidiation, and appressorium formation. magB- transformants, unlike magA- and magC- transformants, exhibited a reduced ability to infect and colonize susceptible rice leaves. G protein alpha subunit genes are required for M. grisea mating. magB- transformants failed to form perithecia, whereas magA- and magC- transformants did not produce mature asci. These results suggest that G protein alpha subunit genes are involved in signal transduction pathways in M. grisea that control vegetative growth, conidiation, conidium attachment, appressorium formation, mating, and pathogenicity.