A Mitogen-Activated Protein Kinase Cascade Regulating Infection-Related Morphogenesis in Magnaporthe grisea  

Abstract

Many fungal pathogens invade plants by means of specialized infection structures called appressoria. In the rice (Oryza sativa) blast fungus Magnaporthe grisea, the pathogenicity mitogen-activated protein (MAP) kinase1 (PMK1) kinase is essential for appressorium formation and invasive growth. In this study, we functionally characterized the MST7 and MST11 genes of M. grisea that are homologous with the yeast MAP kinase kinase STE7 and MAP kinase kinase kinase STE11. Similar to the pmk1 mutant, the mst7 and mst11 deletion mutants were nonpathogenic and failed to form appressoria. When a dominant MST7 allele with S212D and T216E mutations was introduced into the mst7 or mst11 mutant, appressorium formation was restored in the resulting transformants. PMK1 phosphorylation also was detected in the vegetative hyphae and appressoria of transformants expressing the MST7 S212D T216E allele. However, appressoria formed by these transformants failed to penetrate and infect rice leaves, indicating that constitutively active MST7 only partially rescued the defects of the mst7 and mst11 mutants. The intracellular cAMP level was reduced in transformants expressing the MST7 S212D T216E allele. We also generated MST11 mutant alleles with the sterile alpha motif (SAM) and Ras-association (RA) domains deleted. Phenotype characterizations of the resulting transformants indicate that the SAM domain but not the RA domain is essential for the function of MST11. These data indicate that MST11, MST7, and PMK1 function as a MAP kinase cascade regulating infection-related morphogenesis in M. grisea. Although no direct interaction was detected between PMK1 and MST7 or MST11 in yeast two-hybrid assays, a homolog of yeast STE50 in M. grisea directly interacted with both MST7 and MST11 and may function as the adaptor protein for the MST11-MST7-PMK1 cascade.

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

“…Ste50 is an adaptor that links G protein-associated Cdc42-Ste20 complex to the MAPKKK Ste11 through the presence of a Sterile Alpha Motif (SAM) and a Ras Association (RA) domain (Wu et al, 1999). The SAM domain of the M. grisea orthologue Mst50 was previously shown to be essential for its interaction with Mst11 and for appressorium formation (Zhao et al, 2005). Interestingly, Ste50 orthologues of the basidiomycetes U. maydis (Ubc2) and C. neoformans are approximately double in size and contain a Src Homology 3 (SH3) domain which is lacking in the ascomycete Ste50 proteins.…”

“…Orthologues of the MAPKK Ste7 were detected in all species. Fuz7 and Mst7 were previously shown to be required for mating and virulence in U. maydis (Banuett and Herskowitz, 1994) and M. grisea (Zhao et al, 2005). In S. cerevisiae, two MAPKs regulate distinct signalling outputs downstream of Ste7.…”

The Tig1 Histone Deacetylase Complex Regulates Infectious Growth in the Rice Blast Fungus Magnaporthe oryzae

“…Mycelia harvested from 2-d-old 53YEG (0.5% yeast extract and 1% glucose) cultures shaken at 150 rpm were used for isolation of genomic DNA and protoplasts (Sweigard et al, 1998;Zhao et al, 2005). Hygromycin-or zeocin-resistant transformants were selected on media supplemented with 250 mg/mL hygromycin B or 150 mg/mL zeocin (Invitrogen).…”

The Same Receptor, G Protein, and Mitogen-activated Protein Kinase Pathway Activate Different Downstream Regulators in the Alternative White and Opaque Pheromone Responses ofCandida albicans

“…These alternative signals are then transduced through the same heterotrimeric G protein to activate the same MAP kinase pathway, which in turn activates the same downstream regulators that elicit similar mating responses, including G1 arrest, polarization, and shmooing (Sprague et al, 1983;Bender and Sprague, 1986;Leberer et al, 1997). Other fungi, including Magnaporthe grisea (Dixon et al, 1999;Zhao et al, 2005b) Neurospora crassa (Li et al, 2005), and Cryptococcus neoformans (Davidson et al, 2003;Kraus et al, 2003;Bahn et al, 2005) also use MAP kinase pathways for a variety of responses (Kruppa and Calderone, 2006).…”

“…These alternative signals are then transduced through the same heterotrimeric G protein to activate the same MAP kinase pathway, which in turn activates the same downstream regulators that elicit similar mating responses, including G1 arrest, polarization, and shmooing (Sprague et al, 1983;Bender and Sprague, 1986;Leberer et al, 1997). Other fungi, including Magnaporthe grisea (Dixon et al, 1999;Zhao et al, 2005b) Neurospora crassa (Li et al, 2005), and Cryptococcus neoformans (Davidson et al, 2003;Kraus et al, 2003;Bahn et al, 2005) also use MAP kinase pathways for a variety of responses (Kruppa and Calderone, 2006).The pathogenic yeast Candida albicans also uses MAP kinase pathways in the mating process (Chen et al, 2002;Magee et al, 2002), filamentation (Liu et al, 1994;Csank et al, 1998;Navarro-Garcia et al, 1998), and osmoregulation (Alonso-Monge et al, 1999;Smith et al, 2004). But C. albicans has one additional and unique response to mating pheromones that so far has not been identified in other yeast .…”