The induction of sexual development and virulence in the smut fungus Ustilago maydis depends on Crk1, a novel MAPK protein

Abstract

MAP kinases (mitogen-activated protein kinases) are activated by dual phosphorylation on specific threonine and specific tyrosine residues that are separated by a single residue, and the TXY activation motif is a hallmark of MAP kinases. In the fungus Ustilago maydis, which causes corn smut disease, the Crk1 protein, a kinase previously described to have roles in morphogenesis, carries a TXY motif that aligns with the TXY of MAP kinases. In this work, we demonstrate that Crk1 is activated through a mechanism that requires the phosphorylation of this motif. Our data show that Fuz7, a MAPK kinase involved in mating and pathogenesis in U. maydis, is required to activate Crk1, most likely through phosphorylation of the TXY motif. Consistently, we found that Crk1 is also required for mating and virulence. We investigated the reasons for sterility and avirulence of crk1-deficient cells, and we found that Crk1 is required for transcription of prf1, a central regulator of mating and pathogenicity in U. maydis. Crk1 belongs to a wide conserved protein group, whose members have not been previously defined as MAP kinases, although they carry TXY motifs. On the basis of our data, we propose that all of these proteins constitute a new family of MAP kinases.

The MAP kinase Mkc1p is activated under different stress conditions in Candida albicans

“…These antibodies recognize the phosphorylated forms of S. cerevisiae Slt2p, Fus3p and Kss1p (p42-44-related MAP kinases) (Bardwell et al, 1996;Martín et al, 2000), Schizosaccharomyces pombe Spm1 (Zaitsevskaya-Carter & Cooper, 1997) and Ustilago maydis Crk1 (Garrido et al, 2004). In C. albicans, these antibodies should also detect the simultaneous phosphorylation at the threonine and tyrosine residues of the TEY signature of the Mkc1p, Cek1p and Cek2p proteins (a motif absent in other C. albicans MAP kinases).…”

Investigating Host Induced Meiosis in a Fungal Plant Pathogen

“…In addition, Fuz7 (a MAPKK) is required for activation of Crk1. FUZ7 phosphorylates CRK1, activating it (Garrido et al, 2004). Thus Crk1 is clearly involved in the integration of the cAMP and MAPK signalling pathways.…”

“…The link between PRF1 and CRK1 is that CRK1 is required for transcriptional activation of Prf1 through the UAS (Garrido et al, 2004). This provides another avenue for Prf1 control by MAPK and cAMP.…”

“…The MAPK pathway, conversely, positively regulates Crk1 expression, with Kpp2 (a MAPK) mutants resulting in much lower levels of Crk1 in the cell (Garrido & Pérez-Martín, 2003). KPP2 also interacts physically with CRK1, and is required for the role of CRK1 in cell morphogenesis (Garrido et al, 2004). In addition, Fuz7 (a MAPKK) is required for activation of Crk1.…”

“…Crk1 is a target of environmental stimuli in U. maydis: Crk1 mutants are impaired in their response to environmental signals, and Crk1 is highly expressed when cells are grown in nutrition stress conditions (Garrido & Pérez-Martín, 2003). Crk1 also plays a role in mating and pathogenesis since Crk1 mutants are unable to mate on plates and have attenuated pathogenesis producing few tumours and no observed black teliospores (Garrido et al, 2004). Crk1 is also involved in cell morphogenesis.…”