ChMCO1 of Cochliobolus heterostrophus is a new class of metallo-oxidase, playing an important role in DHN-melanization

A metallo-oxidase gene from a phytopathogenic filamentous fungus, Cochliobolus heterostrophus was cloned. Structural prediction of ChMco1 indicated that this protein lacks a transmembrane helix and is soluble, whereas other known fungal metallo-oxidases including Saccharomyces cerevisiae FET3 are localized to the cell membrane. The results of searches in fungal genomic databases and phylogenetic analysis of fungal metallo-oxidases revealed that ChMco1 and its allies are distinct homologues of Fet3 and unique to filamentous ascomycetous species including C. heterostrophus. We performed a functional analysis of ChMCO1 by generating null mutants for the ChMco1 gene. The ChMco1 null (∆ChMco1) mutants clearly had reduced melanization, although they showed normal growth and conidiation. Results also show that ∆ChMco1 mutants lost laccase activity. These results suggest that ChMCO1 is a novel class of metallo-oxidase that is necessary for laccase activity and melanization.