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A mitogen-activated protein kinase cascade regulating infection-related morphogenesis in Magnaporthe grisea

Xinhua Zhao1, Yangseon Kim, Gyungsoon Park

  • 1Department of Botany and Plant Pathology, Purdue University, West Lafayette, Indiana 47907, USA.

The Plant Cell
|March 8, 2005
PubMed

Insights

The MST11-MST7-PMK1 MAP kinase cascade is crucial for rice blast fungus appressorium formation and plant infection. Its components regulate infection-related morphogenesis, with STE50 acting as a potential adaptor protein.

Area of Science:

  • Plant Pathology
  • Molecular Mycology
  • Signal Transduction

Background:

  • Fungal pathogens like Magnaporthe grisea form specialized appressoria to invade plants.
  • The pathogenicity mitogen-activated protein kinase 1 (PMK1) is essential for appressorium development and invasive growth in M. grisea.
  • Understanding the signaling pathways regulating these processes is key to controlling plant diseases.

Purpose of the Study:

  • To functionally characterize the MST7 and MST11 genes in M. grisea, homologous to yeast STE7 and STE11.
  • To elucidate the roles of MST11, MST7, and PMK1 in a MAP kinase cascade controlling infection-related morphogenesis.
  • To identify potential adaptor proteins involved in this signaling pathway.

Main Methods:

  • Gene deletion and allelic replacement of MST7 and MST11 in M. grisea.
  • Introduction of dominant active MST7 alleles and domain-deleted MST11 alleles.
  • Phenotypic analysis of mutants, including appressorium formation and pathogenicity assays.
  • Detection of PMK1 phosphorylation and intracellular cAMP levels.
  • Yeast two-hybrid assays to investigate protein interactions.

Main Results:

  • Deletion mutants of MST7 and MST11 were nonpathogenic and failed to form appressoria, similar to pmk1 mutants.
  • A constitutively active MST7 allele partially restored appressorium formation but not full pathogenicity, and reduced cAMP levels.
  • The sterile alpha motif (SAM) domain of MST11, but not the Ras-association (RA) domain, is essential for its function.
  • A Magnaporthe grisea STE50 homolog directly interacted with MST7 and MST11, suggesting its role as an adaptor protein.

Conclusions:

  • MST11, MST7, and PMK1 function as a MAP kinase cascade regulating infection-related morphogenesis in M. grisea.
  • The STE50 homolog may act as an adaptor protein, mediating interactions within the MST11-MST7-PMK1 cascade.
  • This signaling pathway is critical for the pathogenicity of the rice blast fungus.

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