Two Novel Transcriptional Regulators Are Essential for Infection-related Morphogenesis and Pathogenicity of the Rice Blast Fungus Magnaporthe oryzae

Abstract

The cyclic AMP-dependent protein kinase A signaling pathway plays a major role in regulating plant infection by the rice blast fungus Magnaporthe oryzae. Here, we report the identification of two novel genes, MoSOM1 and MoCDTF1, which were discovered in an insertional mutagenesis screen for non-pathogenic mutants of M. oryzae. MoSOM1 or MoCDTF1 are both necessary for development of spores and appressoria by M. oryzae and play roles in cell wall differentiation, regulating melanin pigmentation and cell surface hydrophobicity during spore formation. MoSom1 strongly interacts with MoStu1 (Mstu1), an APSES transcription factor protein, and with MoCdtf1, while also interacting more weakly with the catalytic subunit of protein kinase A (CpkA) in yeast two hybrid assays. Furthermore, the expression levels of MoSOM1 and MoCDTF1 were significantly reduced in both Δmac1 and ΔcpkA mutants, consistent with regulation by the cAMP/PKA signaling pathway. MoSom1-GFP and MoCdtf1-GFP fusion proteins localized to the nucleus of fungal cells. Site-directed mutagenesis confirmed that nuclear localization signal sequences in MoSom1 and MoCdtf1 are essential for their sub-cellular localization and biological functions. Transcriptional profiling revealed major changes in gene expression associated with loss of MoSOM1 during infection-related development. We conclude that MoSom1 and MoCdtf1 functions downstream of the cAMP/PKA signaling pathway and are novel transcriptional regulators associated with cellular differentiation during plant infection by the rice blast fungus.

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

“…For instance, MoSOM 1 which is a transcription factor serves as a phosphorylation target for CpkA along the cAMP/PKA pathway in M. oryzae . The physical interaction between MoSom1 and CpkA occurs in the presence of cAMP (Yan et al 2011). MoSom1 also interacts with two other transcription factors namely MoCdtf1 and MoStu1 to regulate appressorium initiation and turgor generation and pathogenesis of M. oryzae .…”

“…MoSom1 also interacts with two other transcription factors namely MoCdtf1 and MoStu1 to regulate appressorium initiation and turgor generation and pathogenesis of M. oryzae . More so, MoCDTF1, MoSOM1 and MoMSB2 are also involved in the regulation of sporulation and development of functional appressorium in M. oryzae (Yan et al 2011). Subsequently, ∆ mosom 1 and ∆ mocdtf 1 strains were non-pathogenic and failed to induce lesions on both susceptible rice and barley seedlings (Yan et al 2011).…”

“…More so, MoCDTF1, MoSOM1 and MoMSB2 are also involved in the regulation of sporulation and development of functional appressorium in M. oryzae (Yan et al 2011). Subsequently, ∆ mosom 1 and ∆ mocdtf 1 strains were non-pathogenic and failed to induce lesions on both susceptible rice and barley seedlings (Yan et al 2011). Mst12 represents one of the well-studied transcription factors which is phosphorylated by the Pmk1-MAPK (Hamel et al 2012).…”

Temporal Analysis of the Magnaporthe Oryzae Proteome During Conidial Germination and Cyclic AMP (cAMP)-mediated Appressorium Formation

“…A yeast two hybrid assay identified seven proteins that interact directly with CpkA (15). Recently, the expression of two transcriptional regulators, CDTF1 and SOM1, was reported to be reduced in mac1 and cpkA mutants with Som1 also being shown to interact weakly with CpkA (16). Mutational analysis of these two genes indicated that each has multiple pleiotrophic effects on growth and development in M. oryzae (16).…”

“…Recently, the expression of two transcriptional regulators, CDTF1 and SOM1, was reported to be reduced in mac1 and cpkA mutants with Som1 also being shown to interact weakly with CpkA (16). Mutational analysis of these two genes indicated that each has multiple pleiotrophic effects on growth and development in M. oryzae (16). Furthermore, a total of 110 cAMP responsive sequence tags were identified in a SAGE analysis of conidia following cAMP treatment of which 60 (50 up-regulated and 10 down-regulated) were assigned to a gene or expressed sequence tag (17).…”