MADS-Box Transcription Factor Mig1 Is Required for Infectious Growth in Magnaporthe grisea

Abstract

Magnaporthe grisea is a model fungus for studying fungus-plant interactions. Two mitogen-activated protein (MAP) kinase genes, PMK1 and MPS1, have been implicated in regulating plant infection processes in M. grisea. However, transcription factors activated by these MAP kinases are not well studied. In this study we functionally characterized the MIG1 gene that encodes a MADS-box transcription factor homologous to Saccharomyces cerevisiae Rlm1. In yeast two-hybrid assays, MIG1 interacts with MPS1, suggesting that MIG1 may function downstream from the MPS1 pathway. The mig1 deletion mutant had a normal growth rate and formed melanized appressoria, but it was nonpathogenic and failed to infect rice leaves through wounds. Appressoria formed by the mig1 mutant developed penetration pegs and primary infectious hyphae, but further differentiation of the secondary infectious hyphae inside live plant cells was blocked. However, the mig1 mutant formed infectious hypha-like structures in heat-killed plant cells or cellophane membranes. In transformants expressing the MIG1-GFP fusion, green fluorescent protein (GFP) signals were not detectable in vegetative hyphae and conidiophores. Mig1-GFP was localized to nuclei in conidia, appressoria, and infectious hyphae. Deletion of the MADS box had no effect on the expression and localization of the MIG1-GFP fusion but eliminated its ability to complement the mig1 mutant. These results suggest that MIG1 may be required for overcoming plant defense responses and the differentiation of secondary infectious hyphae in live plant cells. The MADS-box domain is essential for the function of MIG1 but dispensable for its nuclear localization, which may be associated with the activation of MIG1 by MPS1 during conidiation and plant infection.Magnaporthe grisea is an economically important fungal pathogen that invades crops such as rice, barley, wheat, and millet. Rice blast, caused by this heterothallic haploid ascomycete, is one of the most severe fungal diseases of rice throughout the world, and it has been developed as a model system to study fungus-plant interactions (11, 39). M. grisea was the first plant pathogenic fungus to be sequenced (8). The infection process of this pathogen is initiated by the germination of conidia attached to the plant surface and the development of a highly specialized infection structure called an appressorium. Direct penetration of the underlying plant surface is achieved by the generation of enormous turgor pressure in the appressorium (9). After penetration, the penetration peg differentiates into an unbranched primary infectious hypha, which in turn differentiates into bulbous, lobed secondary infectious hyphae. Initially, the fungus grows biotrophically in infected plant tissues but eventually causes typical blast lesions (20).In the past decade, several signal transduction pathways involved in the regulation of different plant infection processes have been characterized in M. grisea (42). The cyclic AMP (cAMP) signaling pathway is required for surface ...

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

“…It is also essential for root infection (Sesma and Osbourn, 2004) and the proper regulation of the mobilization of storage carbohydrate and lipid reserves from conidia to appressoria (Thines et al, 2000). The other MAP kinase pathway essential for pathogenesis in M. oryzae is the MPS1 cascade, which is dispensable for appressorium formation but required for appressorial penetration (Xu et al, 1998;Jeon et al, 2008;Mehrabi et al, 2008). These two pathways also have been shown to be important for plant infection in other phytopathogenic fungi, including some species that do not form appressoria (Rispail et al, 2009).…”

“…In the past decade, there have been extensive studies on the molecular mechanisms that regulate appressorium morphogenesis and penetration in M. oryzae Wilson and Talbot, 2009). In addition to ALB1, BUF1, and RSY1, which are required for melanin synthesis, many genes that are important for appressorium formation and penetration have been characterized (Ebbole, 2007;Xu et al, 2007), including PTH12, MMT1, TPS1, CYP1, PLS1, MIG1, and MHP1 (Clergeot et al, 2001;Tucker et al, 2004;Wilson et al, 2007;Mehrabi et al, 2008;Kim et al, 2009). Among these genes found to be important for early plant infection processes are several components of cAMP signaling and two mitogen-activated protein (MAP) kinase pathways.…”

Regulatory network of genes associated with stimuli sensing, signal transduction and physiological transformation of appressorium in Magnaporthe oryzae

“…The deletion of MoMCM 1 phenotyping the mst12 mutant produced appressoria unable to penetrate the plant surface effectively. The two downstream targets of Mps1 MAPK cascade are Mig1 and Swi6 essential in regulating appressorium morphogenesis and cell wall integrity (Shiozaki and Russell 1996; Mehrabi et al 2008; Qi et al 2012). Targeted gene deletion of MoSW I6 compromised the cell wall integrity and suppressed the expression of extracellular enzymes implicated in the maintenance of cell wall rigidity during host penetration.…”

Molecular mechanisms regulating plant infection in the rice blast fungus Magnaporthe oryzae

“…MIG1 is involved in the late stages of M. oryzae infection since the Δmig1 mutants form normal appressoria, penetrate host cells and develop primary IH but fail to infect wounded leaves. Mig1 is one of the two MADS-box transcription factors present in M. oryzae and a downstream target of the MAPK Mps1 (Mehrabi, et al, 2008). The MIR1 gene specifically expressed in M. oryzae IH encodes a protein of unknown function, which is present only in the M. oryzae species complex.…”

“…MoMsb2 together with Cbp1 recognize extracellular signals that lead to Ras2 activation. In addition, several transcription factors regulated by Pmk1 have been described such as Mst12 , Mig1 (Mehrabi, et al, 2008), MoSLF and MoMcm1 .…”