Identification of fuz7, a Ustilago maydis MEK/MAPKK homolog required for a-locus-dependent and -independent steps in the fungal life cycle.
Ustilago maydis is a plant pathogenic Basidiomycete fungus that exhibits dimorphism--it 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.
Banuett
F
F
Department of Biochemistry and Biophysics, School of Medicine, University of California San Francisco 94143-0448.
Herskowitz
I
I
D000595:Amino Acid Sequence; D001483:Base Sequence; D017871:Calcium-Calmodulin-Dependent Protein Kinases / Q000235:genetics*; D004171:Diploidy; D005656:Fungal Proteins; D005800:Genes, Fungal / Q000235:genetics*; D049770:Genes, Mating Type, Fungal; D006238:Haploidy; D000072235:Mating Factor; D020929:Mitogen-Activated Protein Kinase Kinases; D008954:Models, Biological; D008969:Molecular Sequence Data; D009024:Morphogenesis; D009154:Mutation; D010455:Peptides / Q000378:metabolism; D010941:Plant Tumors / Q000382:microbiology; D011494:Protein Kinases / Q000235:genetics; D012098:Reproduction; D017386:Sequence Homology, Amino Acid; D015398:Signal Transduction; D013172:Spores, Fungal / Q000254:growth & development; D014588:Ustilago / Q000166:cytology / Q000235:genetics* / Q000254:growth & development* / Q000472:pathogenicity; D003313:Zea mays / Q000382:microbiology
D005656:Fungal Proteins; D010455:Peptides; D000072235:Mating Factor; D011494:Protein Kinases; D017871:Calcium-Calmodulin-Dependent Protein Kinases; C089988:Fuz7 protein, Ustilago maydis; D020929:Mitogen-Activated Protein Kinase Kinases