MST12 Regulates Infectious Growth But Not Appressorium Formation in the Rice Blast Fungus Magnaporthe grisea

Abstract

In the rice blast fungus Magnaporthe grisea, a mitogen-activated protein kinase gene, PMK1, is known to regulate appressorium formation and infectious hyphae growth. Since PMK1 is homologous to the FUS3 and KSS1 genes that regulate the transcription factor STE12 in yeast, we functionally characterized the STE12 homologue in M. grisea (MST12). A polymerase chain reaction-based approach was used to isolate the MST12 gene that is homologous to yeast STE12. Four mst12 deletion mutants were isolated by gene replacement. No obvious defect in vegetative growth, conidiation, or conidia germination was observed in mst12 mutants. However, mst12 mutants were nonpathogenic on rice and barley leaves. In contrast to pmk1 mutants that did not form appressoria, mst12 mutants produced typical dome-shaped and melanized appressoria. However, the appressoria formed by mst12 mutants failed to penetrate onion epidermal cells. When inoculated through wound sites, mst12 mutants failed to cause spreading lesions and appeared to be defective in infectious growth. These data indicate that MST12 may function downstream of PMK1 to regulate genes involved in infectious hyphae growth. A transcription factor or factors other than MST12 must exist in M. grisea and function downstream from PMK1 for appressorium formation.

Early Colony Establishment in Neurospora crassa Requires a MAP Kinase Regulatory Network

“…In filamentous fungi, Ste12-like proteins possess two C2H2-Zn 2+ motifs, in addition to the well-conserved homeodomain-like STE domain (Park et al 2002). The STE domain is essential for function and DNA binding in S. cerevisiae (Yuan and Fields 1991).…”

“…After Fus3 is activated, it enters the nucleus and phosphorylates Ste12, a mating-type-specific transcription factor, as well as two regulators of Ste12, Dig1 and Dig2 (Blackwell et al 2007). Activated Ste12 regulates the expression of many genes involved in the mating process, both indirectly and directly by binding pheromone response elements in target promoters (Zeitlinger et al 2003).Ste12-like proteins have also been studied in filamentous fungi, where they play essential roles in development and pathogenicity (Alspaugh et al 1998;Vallim et al 2000;Borneman et al 2001;Park et al 2002;Tsuji et al 2003;Li et al 2005;Nolting and Poggeler 2006;Ren et al 2006;Tollot et al 2009;Rispail and Di Pietro 2010;Wong Sak Hoi and Dumas 2010). Fus3-like proteins in filamentous fungi could directly or indirectly phosphorylate Ste12-like proteins, but this has not yet been shown in any system.…”

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

“…We therefore decided to investigate Sec6 localization in a Dmst12 mutant. MST12 encodes a transcription factor that acts downstream of the Pmk1 MAPK pathway of M. oryzae and is required for septin ring formation and plant infection (Park et al, 2002;Dagdas et al, 2012). Sec6-GFP was completely mislocalized in mature appressoria of a Dmst12 mutant (Figure 5; Supplemental Figure 11).…”

An STE12 gene identified in the mycorrhizal fungus Glomus intraradices restores infectivity of a hemibiotrophic plant pathogen

“…In situ RT-PCR experiments localized transcripts of GintSTE not only within cytoplasm of spores but also in cytoplasm of germination hyphae. Such a high level of expression may reflect a more general role of GintSTE in the control of processes, leading to spore germination, similar to that of CST1 involved in conidia germination in C. lagenarium (Park et al, 2002). C. lindemuthianum wild-type (β) and clste12Δ (B77) strains were transformed with pDHT GintSTE construct (B77G5, B77G6) or pDHT empty vector (βv, B77v).…”