Multiple Upstream Signals Converge on the Adaptor Protein Mst50 in Magnaporthe grisea

Abstract

Rice blast fungus (Magnaporthe grisea) forms a highly specialized infection structure for plant penetration, the appressorium, the formation and growth of which are regulated by the Mst11-Mst7-Pmk1 mitogen-activated protein kinase cascade. We characterized the MST50 gene that directly interacts with both MST11 and MST7. Similar to the mst11 mutant, the mst50 mutant was defective in appressorium formation, sensitive to osmotic stresses, and nonpathogenic. Expressing a dominant active MST7 allele in mst50 complemented its defects in appressorium but not lesion formation. The sterile a-motif (SAM) domain of Mst50 was essential for its interaction with Mst11 and for appressorium formation. Although the SAM and Ras-association domain (RAD) of Mst50 were dispensable for its interaction with Mst7, deletion of RAD reduced appressorium formation and virulence on rice (Oryza sativa) seedlings. The interaction between Mst50 and Mst7 or Mst11 was detected by coimmunoprecipitation assays in developing appressoria. Mst50 also interacts with Ras1, Ras2, Cdc42, and Mgb1 in yeast two-hybrid assays. Expressing a dominant active RAS2 allele in the wild-type strain but not in mst50 stimulated abnormal appressorium formation. These results indicate that MST50 functions as an adaptor protein interacting with multiple upstream components and plays critical roles in activating the Pmk1 cascade for appressorium formation and plant infection in M. grisea.

Comparative genomics of MAP kinase and calcium–calcineurin signalling components in plant and human pathogenic fungi

“…In U. maydis, expression of a dominant active allele of the ras2 orthologue promoted pseudohyphal growth in a manner dependent on the pheromone-response MAPK cascade (Lee and Kronstad, 2002). Likewise, expression of a dominant active ras2 allele of M. grisea stimulated appressorium formation on non-inductive surfaces in the wild-type strain, but not in the pmk1 mutant, suggesting that Ras2 functions upstream of the Mst11-Mst7-Pmk1 cascade (Park et al, 2006). A similar signalling role for Ras2 was proposed in F. graminearum (Bluhm et al, 2007).…”

Autophagy vitalizes the pathogenicity of pathogenic fungi

“…Deletion of MST50 leads to inability to form appressoria and thus loss of pathogenicity. 52 While it is clear that this signaling pathway contributes to the development of the infection structure, as yet there are no data available that specifically link it with autophagy in plant pathogenic fungi (Fig. 2).…”

Septin-Dependent Assembly of the Exocyst Is Essential for Plant Infection by Magnaporthe oryzae

“…In M. oryzae, the Pmk1 pathway is regulated through upstream components, including the MAPK kinase kinase Mst11, MAPK kinase Mst7, and an adaptor protein, Mst50 (Zhao et al, 2005;Park et al, 2006;Wilson and Talbot, 2009). The adaptor protein, Mst50, directly interacts with Cdc42 and the Ras2 GTPase, (A) Temperature sensitivity of the sec6 Y601P mutant was tested by comparison of hyphal growth of an ectopic transformant (sec6-2) and wild-type Guy11 after incubation at the semirestrictive temperature of 29°C for 4 d and restoration of hyphal growth was done by incubation for a further 3 d at 24°C.…”