Characterization of MST11, a MEK kinase gene in the rice blast fungus, Magnaporthe grisea

Yangseon Kim, Purdue University

Abstract

Rice blast, a devastating disease on rice worldwide, is caused by heterothallic haploid ascomycete Magnaporthe grisea. On plant leaves or artificial hydrophobic surfaces, germ tubes produced from conidia differentiate into specialized infection structures called appressoria. The fungus then uses enormous turgor pressure generated in appressoria for plant penetration. In M. grisea, the Pmk1 MAP kinase regulates appressorium formation and plant infection. MST11 encodes a MEK kinase that is homologous to yeast STE11. The mst11 deletion mutants failed to form appressoria and penetrate plant cells. MST11 has a sterile alpha motif (SAM), Ras association (RA) domain, two putative phosphorylation sites, and a protein kinase domain. The SAM of Mst11 was essential for its interaction with Mst50 and activities. In contrast, deletion of the RA domain had no effect on appressorium formation but was reduced in the efficiency of appressorial penetration and virulence. Multiple appressoria were formed by branching germ tubes in the MST11ΔRA transformants. The two putative phosphorylation sites and the self-inhibitory interaction between the N-terminal region and the kinase domain of MST11 also were functionally characterized. We also examined the interaction between Mst11 and Ras proteins and determined the effect of a putative dominant active mutation. Results from these studies indicate that MST11 encodes a MEK kinase that plays a critical role in the activation of the PMK1 MAP kinase pathway.

Degree

Ph.D.

Advisors

Xu, Purdue University.

Subject Area

Plant Pathology

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