Disruption of two genes for chitin synthase in the phytopathogenic fungus Ustilago maydis

Summary The phytopathogenic fungus Ustilago maydis exhibits a dimorphic transition in which non‐pathogenic, yeast‐like cells mate to form a pathogenic, filamentous dikaryon. Northern analysis indicated that two chitin synthase genes, chs1 and chs2 , from U. maydis are expressed at similar levels in yeast‐like cells and in cells undergoing the mating reaction leading to the filamentous cell type. A mutation was constructed in each of the chitin synthase genes by targeted gene disruption. Each mutant showed a reduction in the level of trypsin‐activated enzyme activity, compared with a wild‐type strain, but retained the wild‐type morphology, the ability to mate and the ability to form the filamentous pathogenic cell type.