Identification of fuz7, a Ustilago maydis MEK/MAPKK homolog required for a-locus-dependent and -independent steps in the fungal life cycle.

Abstract

Ustilago maydis is a plant pathogenic Basidiomycete fungus that exhibits dimorphismuit has a haploid, yeast-like phase and a dikaryotic, filamentous phase that is pathogenic. Establishment and maintenance of these two forms are controlled by two mating type loci, a and b. The a locus is thought to govern fusion of haploid cells to form a dikaryon and is also required for filamentous growth of the dikaryon. It encodes two components of a pheromone response pathway: pheromones and receptors. We report the identification of the U. maydis fuz7 gene, which codes for a putative dual specificity serine/threonine tyrosine kinase of the MAP kinase kinase (MAPKK/MEK) family, by homology with other members of the family. Analysis of mutants deleted for fuz7 shows that it participates in different facets of the life cycle: It is necessary for a-locus-dependent processes, such as conjugation tube formation, filament formation, and maintenance of filamentous growth, and for a-locus-independent processes, such as tumor induction and teliospore germination, fuz7 is the first U. maydis gene distinct from the b locus required for fungal pathogenicity. We propose that fuz7 is involved in at least two pathways, one of which responds to the pheromones coded by the a locus and the other to putative signals from the plant.

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

“…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.…”

Ustilago maydis – a valuable model system for the study of fungal dimorphism and virulence

“…Interestingly, two of these components have also been identified as members of the pheromone signalling pathway. Ubc5 is identical to Fuz7 (Banuett & Herskowitz, 1994), which has been suggested to be involved in pheromone signalling, and Ubc3 is identical to Kpp2, which has been identified as MAPK, being part of the pheromone response pathway (Mu$ ller et al, 1999).…”

Fungal physiology and the origins of molecular biology

“…Flora Banuett and her colleagues have studied the U. maydis yeast-like non-pathogenic form and filamentous pathogenic form, finding that the fuz1 gene encodes a Znfinger domain protein that through interactions with other proteins regulates specific transcriptional activity and morphogenesis (Banuett & Herskowitz, 1994). Disruption of genes encoding adenylate cyclase or the catalytic subunit of cAMP-dependent protein kinase led to constitutive filamentous growth, which could be suppressed by the lack of MAPKK (Fuz7), leading to the suggestion that morphogenesis in this organism is regulated by both cAMP and MAP kinase signal transduction pathways, reminiscent of the much earlier observations with the phycomycete M. rouxii.…”