The UmGcn5 gene encoding histone acetyltransferase from Ustilago maydis is involved in dimorphism and virulence

• First report of the relationship between histone acetylation and fungal pathogenesis.
• First report of the relationship between a histone acetyltransferase and fungal dimorphism (as a cellular differentiation process).
• Observation that pathogenesis and dimorphism in Ustilago maydis have an epigenetic regulation background.

We isolated a gene encoding a histone acetyltransferase from Ustilago maydis (DC.) Cda., which is orthologous to the Saccharomyces cerevisiae GCN5 gene. The gene was isolated from genomic clones identified by their specific hybridization to a gene fragment obtained by the polymerase chain reaction (PCR). This gene (Umgcn5; um05168) contains an open reading frame (ORF) of 1421 bp that encodes a putative protein of 473 amino acids with a Mr. of 52.6 kDa. The protein exhibits a high degree of homology with histone acetyltransferases from different organisms. Null a2b2 ΔUmgcn5 mutants were constructed by substitution of the region encoding the catalytic site with a hygromycin B resistance cassette. Null a1b1 ΔUmgcn5 mutants were isolated from genetic crosses of a2b2 ΔUmgcn5 and a1b1 wild-type strains in maize. Mutants displayed a slight reduction in growth rate under different conditions, and were more sensitive than the wild type to stress conditions, but more important, they grew as long mycelial cells, and formed fuzz-like colonies under all conditions where wild-type strains grew in the yeast-like morphology and formed smooth colonies. This phenotype was not reverted by cAMP addition. Mutants were not virulent to maize plants, and were unable to form teliospores. These phenotypic alterations of the mutants were reverted by their transformation with the wild-type gene.