Fuz1, a MYND domain protein, is required for cell morphogenesis in Ustilago maydis

Abstract

Ustilago maydis is a Basidiomycete fungus that exhibits a yeast-like nonpathogenic form and a dikaryotic filamentous pathogenic form. Generation of these two forms is controlled by two mating type loci, a and b. The fungus undergoes additional morphological transitions in the plant that result in formation of a third cell type, the teliospore. The fuz1 gene is necessary for this developmental program. Here we report cloning and sequencing of fuz1 and show that it contains an open reading frame with coding capacity for a protein of 1421 amino acids. The Fuz1 protein belongs to the family of MYND Zn finger domain proteins. We generate a null mutation in strains of opposite mating type and show that fuz1 is necessary for conjugation tube formation, a morphological transition that occurs in response to pheromones. We generate fuz1⁻ diploid strains heterozygous at a and b and show that fuz1 is also necessary for postfusion events (maintenance of filamentous growth). We also demonstrate that fuz1 is necessary for cell morphogenesis of the yeast-like cell: normal cell length, location and number of septa, cell separation and constriction of the neck region. Fuz1 is also required for cell wall integrity and to prevent secretion of a dark pigment. We propose that the MYND domain may interact with different proteins to regulate cell morphogenesis.

• cell separation
• conjugation tube
• filamentous growth
• pigment production
• septum location

We thank Bill Holloman for a kind gift of plasmids pCM54 and pCM619, Alan Budde and Sally Leong for a kind gift of plasmid pHL1, Miroslav Vranes and Jörg Kämper for communicating results beforePUBLICation, Michael Feldbrügge and colleagues for a kind gift of the plasmid collection for U. maydis KO, two anonymous reviewers for their comments and suggestions. This work was supported by NIH grants SO6 GM63119 and 2S06 GM063119 to FB. YA was supported by HHMI grant 52002663 for undergraduate research in the Biology Honors Program at CSULB.