title: Two PAK kinase genes, CHM1 and MST20, have distinct functions in Magnaporthe grisea.
abstract: In the rice blast fungus Magnaporthe grisea, the Pmk1 mitogen-activated protein (MAP) kinase is essential for appressorium formation and infectious growth. PMK1 is homologous to yeast Fus3 and Kss1 MAP kinases that are known to be regulated by the Ste20 PAK kinase for activating the pheromone response and filamentation pathways. In this study, we isolated and characterized two PAK genes, CHM1 and MST20, in M. grisea. Mutants disrupted in MST20 were reduced in aerial hyphae growth and conidiation, but normal in growth rate, appressorium formation, penetration, and plant infection. In chm1 deletion mutants, growth, conidiation, and appressorium formation were reduced significantly. Even though appressoria formed by chm1 mutants were defective in penetration, chm1 mutants were able to grow invasively on rice leaves and colonize through wounds. The chm1 mutants were altered in conidiogenesis and produced conidia with abnormal morphology. Hyphae of chm1 mutants had normal septation, but the length of hyphal compartments was reduced. On nutritionally poor oatmeal agar, chm1 mutants were unstable and produced sectors that differed from original chm1 mutants in growth rate, conidiation, or colony morphology. However, none of the monoconidial cultures derived from these spontaneous sectors were normal in appressorial penetration and fungal pathogenesis. These data suggest that MST20 is dispensable for plant infection in M. grisea, but CHM1 plays a critical role in appressorium formation and penetration. Both mst20 and chm1 deletion mutants were phenotypically different from the pmk1 mutant that is defective in appressorium formation and infectious hyphae growth. It is likely that MST20 and CHM1 individually play no critical role in activating the PMK1 MAP kinase pathway during appressorium formation and infectious hyphae growth. However, CHM1 appears to be essential for appressorial penetration and CHM1 and MST20 may have redundant functions in M. grisea.
authors.affiliation: Department of Botany and Plant Pathology, Purdue University, West Lafayette, IN 47907, USA.
authors.forename: Lei
authors.initials: L
authors.lastname: Li
authors.forename: Chaoyang
authors.initials: C
authors.lastname: Xue
authors.forename: Kenneth
authors.initials: K
authors.lastname: Bruno
authors.forename: Marie
authors.initials: M
authors.lastname: Nishimura
authors.forename: Jin-Rong
authors.initials: JR
authors.lastname: Xu
mesh_terms: D005656:Fungal Proteins / Q000235:genetics / Q000378:metabolism; D056229:Fungal Structures / Q000201:enzymology / Q000235:genetics* / Q000254:growth & development; D025301:Hyphae / Q000201:enzymology / Q000235:genetics / Q000254:growth & development; D007113:Immunity, Innate / Q000235:genetics; D047908:Intracellular Signaling Peptides and Proteins; D020930:MAP Kinase Kinase Kinases; D020082:Magnaporthe / Q000201:enzymology / Q000235:genetics* / Q000254:growth & development; D008969:Molecular Sequence Data; D009154:Mutation; D010641:Phenotype; D010802:Phylogeny; D010935:Plant Diseases / Q000235:genetics / Q000382:microbiology; D018515:Plant Leaves / Q000382:microbiology; D017346:Protein Serine-Threonine Kinases / Q000235:genetics* / Q000378:metabolism; D029701:Saccharomyces cerevisiae Proteins; D017384:Sequence Deletion; D013172:Spores, Fungal / Q000201:enzymology / Q000235:genetics / Q000254:growth & development; D015003:Yeasts / Q000235:genetics / Q000378:metabolism
chemical_list: D005656:Fungal Proteins; D047908:Intracellular Signaling Peptides and Proteins; D029701:Saccharomyces cerevisiae Proteins; C095212:CLA4 protein, S cerevisiae; D017346:Protein Serine-Threonine Kinases; D020930:MAP Kinase Kinase Kinases; C078754:STE20 protein, S cerevisiae