A highly conserved MAPK-docking site in Mst7 is essential for Pmk1 activation in Magnaporthe grisea.
In Magnaporthe grisea, the MST11-MST7-PMK1 MAP kinase (MAPK) cascade is essential for appressorium formation and plant infection. Although expressing a dominant active MST7 allele results in Pmk1 activation in the absence of Mst11 and improper regulation of appressorium formation, the direct interaction between Mst7 and Pmk1 is not observed in yeast two-hybrid assays. Thus, it is not clear how Mst7 transmits the upstream signals to Pmk1. Like its homologues from other ascomycetes, Mst7 contains a putative MAPK-docking site (12-20) at its N-terminus. Deletion of this MAPK-docking site had no obvious effect on the expression of MST7 but blocked appressorium formation and plant infection. The kinase activity of Mst7 was not affected by the docking site deletion but Mst7(Delta12-20) failed to activate Pmk1. Mutations in the putative docking region of Pmk1 also abolished appressorium formation. In both co-immunoprecipitation and bimolecular fluorescence complementation (BiFC) assays, the direct interaction between Mst7 and Pmk1 was detected only during appressorium formation. Deletion of the MAPK-docking site of Mst7 eliminated the Mst7-Pmk1 interaction in M. grisea. These data indicate that the MAPK-docking site of Mst7 is essential for its association and activation of downstream Pmk1, and the Mst7-Pmk1 interaction is enhanced or stabilized during appressorium formation.
Zhao
Xinhua
X
Department of Botany and Plant Pathology, Purdue University, West Lafayette, IN 47907, USA.
Xu
Jin-Rong
JR
D000595:Amino Acid Sequence; D017124:Conserved Sequence; D005656:Fungal Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D017353:Gene Deletion; D015966:Gene Expression Regulation, Fungal; D005816:Genetic Complementation Test; D049452:Green Fluorescent Proteins / Q000235:genetics; D047468:Immunoprecipitation; D020935:MAP Kinase Signaling System; D020082:Magnaporthe / Q000201:enzymology* / Q000378:metabolism; D020928:Mitogen-Activated Protein Kinases / Q000378:metabolism*; D008969:Molecular Sequence Data; D016297:Mutagenesis, Site-Directed; D012275:Oryza / Q000382:microbiology; D010935:Plant Diseases / Q000382:microbiology; D011494:Protein Kinases / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D011993:Recombinant Fusion Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D016415:Sequence Alignment
D005656:Fungal Proteins; D011993:Recombinant Fusion Proteins; D049452:Green Fluorescent Proteins; D011494:Protein Kinases; D020928:Mitogen-Activated Protein Kinases; C102726:Pmk1 protein, Magnaporthe grisea