Regulation of cAMP-dependent protein kinase during appressorium formation in Magnaporthe grisea

Abstract

The rice blast fungus, Magnaporthe grisea, requires formation of an appressorium, a dome-shaped and highly melanized infection structure, to infect its host. cAMP was identified as an important second messenger in signaling systems for appressorium formation in this fungus. To understand further the role of cAMP in infection-related morphogenesis, cAMP-dependent protein kinase activity was measured during appressorium formation and germination of conidia. Much higher activity of protein kinase was detected in germlings forming appressoria on the hydrophobic surface of GelBond than germlings growing vegetatively on a hydrophilic surface. In liquid culture, protein kinase activity increased during conidial germination, and peaked at 8 h after incubation before declining. Two transformants which develop small non-functional appressoria, and which lack cpkA, a gene encoding the catalytic subunit of protein kinase, did not show protein kinase activity. These data suggest that protein kinase has significant roles in the regulation of functional appressorium formation in M. grisea.