Characterization of the sterol 14alpha-demethylases of Fusarium graminearum identifies a novel genus-specific CYP51 function

CYP51 encodes the cytochrome P450 sterol 14-demethylase, an enzyme essential for sterol biosynthesis and the target of azole fungicides. In Fusarium species, including pathogens of humans and plants, three CYP51 paralogues have been identified with one unique to the genus. Currently, the functions of these three genes and the rationale for their conservation within the genus Fusarium are unknown. Three Fusarium graminearum CYP51s (FgCYP51s) were heterologously expressed in Saccharomyces cerevisiae. Single and double FgCYP51 deletion mutants were generated and the functions of the FgCYP51s were characterized invitro and inplanta. FgCYP51A and FgCYP51B can complement yeast CYP51 function, whereas FgCYP51C cannot. FgCYP51A deletion increases the sensitivity of F.graminearum to the tested azoles. In FgCYP51B and FgCYP51BC mutants, ascospore formation is blocked, and eburicol and two additional 14-methylated sterols accumulate. FgCYP51C deletion reduces virulence on host wheat ears. FgCYP51B encodes the enzyme primarily responsible for sterol 14-demethylation, and plays an essential role in ascospore formation. FgCYP51A encodes an additional sterol 14-demethylase, induced on ergosterol depletion and responsible for the intrinsic variation in azole sensitivity. FgCYP51C does not encode a sterol 14-demethylase, but is required for full virulence on host wheat ears. This is the first example of the functional diversification of a fungal CYP51.