Gα and Gβ Proteins Regulate the Cyclic AMP Pathway That Is Required for Development and Pathogenicity of the Phytopathogen Mycosphaerella graminicola

Abstract

We identified and functionally characterized genes encoding three G␣ proteins and one G␤ protein in the dimorphic fungal wheat pathogen Mycosphaerella graminicola, which we designated MgGpa1, MgGpa2, MgGpa3, and MgGpb1, respectively. Sequence comparisons and phylogenetic analyses showed that MgGPA1 and MgGPA3 are most related to the mammalian G␣ i and G␣ s families, respectively, whereas MgGPA2 is not related to either of these families. On potato dextrose agar (PDA) and in yeast glucose broth (YGB), MgGpa1 mutants produced significantly longer spores than those of the wild type (WT), and these developed into unique fluffy mycelia in the latter medium, indicating that this gene negatively controls filamentation. MgGpa3 mutants showed more pronounced yeast-like growth accompanied with hampered filamentation and secreted a dark-brown pigment into YGB. Germ tubes emerging from spores of MgGpb1 mutants were wavy on water agar and showed a nested type of growth on PDA that was due to hampered filamentation, numerous cell fusions, and increased anastomosis. Intracellular cyclic AMP (cAMP) levels of MgGpb1 and MgGpa3 mutants were decreased, indicating that both genes positively regulate the cAMP pathway, which was confirmed because the WT phenotype was restored by adding cAMP to these mutant cultures. The cAMP levels in MgGpa1 mutants and the WT were not significantly different, suggesting that this gene might be dispensable for cAMP regulation. In planta assays showed that mutants of MgGpa1, MgGpa3, and MgGpb1 are strongly reduced in pathogenicity. We concluded that the heterotrimeric G proteins encoded by MgGpa3 and MgGpb1 regulate the cAMP pathway that is required for development and pathogenicity in M. graminicola.

Functional analysis of the G-protein α subunits FGA1 and FGA3 in the banana pathogen Fusarium oxysporum f. sp. cubense

“…Similar results were observed in null mutants of other fungal group II Ga genes, such as gpa2 from U. maydis [12] and mggpa2 from Mycosphaerella graminicola [24]. Interestingly, the Ga gene bcg2 from B. cinerea was found to be involved in the regulation of pathogenicity, and magC was reported to play roles in the modulation of the conidiation and development of asci in M. grisea [6].…”

Mitogen-Activated Protein Kinase Signaling in Plant-Interacting Fungi: Distinct Messages from Conserved Messengers

“…As seen for the Mor-slt2 mutants, Cpu-slt2, Fgr-slt2, Mgr-slt2, and Uma-slt2 mutants all have weakened cell walls and show increased sensitivity to cell wall-degrading enzymes and to compounds interfering with cell wall biosynthesis (Hou et al, 2002;Mey et al, 2002a;Mehrabi et al, 2006a;Carbó and Pérez-Martín, 2010). By contrast, deletion of Slt2 homologs from C. orbiculare and B. cinerea has no obvious effect on cell wall sensitivity to lytic enzymes and inhibitors (Kojima et al, 2002;Rui and Hahn, 2007).…”

“…In B. cinerea, bmp3 (here renamed Bci-slt2) mutants are defective in surface sensing, plant penetration, and induction of necrotic lesions (Rui and Hahn, 2007). In M. graminicola, Slt2 mutants show normal penetration of wheat stomata but are highly reduced in virulence because infectious hyphae fail to branch out (Mehrabi et al, 2006a). Finally, MGV1 (here renamed Fgr-Slt2) was shown to control heterokaryon formation and accumulation of trichothecene mycotoxins in F. graminearum (Hou et al, 2002).…”

Flexible gateway constructs for functional analyses of genes in plant pathogenic fungi

“…2B 0 ). To generate the FT vector for GFP expression in Z. tritici Gpb1 mutant (Mehrabi et al, 2009) and the Z. tritici Wor1 mutant (Mirzadi Gohari et al, 2014), pRM236, pRM251 (geneticin entry vector) and pRM234 were incorporated into pPm43GW generating pFT3 (Fig. 2C 0 ).…”

“…In order to validate the geneticin selection marker, pFT3 and pFT4 were generated to express GFP and RFP, respectively. Both constructs were used to transform Z. tritici strains deleted for Gpb1 (Mehrabi et al, 2009) (FT vectors). To generate each FT vector, three entry vectors were used to recombine the three fragments into the binary destination vector, pPm43GW, generating pFT1 (A 0 ), pFT2 (B 0 ), pFT3 (C 0 ), pFT4 (D 0 ) and pFT5 (E 0 ).…”