Functional Identification of Sterol-4alpha-methyl Oxidase CDNAs from Arabidopsis Thaliana by Complementation of a Yeast Erg25 Mutant Lacking Sterol-4alpha-methyl Oxidation

Specific primers derived from both genomic sequence data and EST cDNA sequences were used to polymerase chain reaction amplify two full-length cDNA sequences (AtSMO1 and AtSMO2), 801 and 783 bp, respectively, from an Arabidopsis thaliana cDNA library. The predicted proteins show 32 and 29% identity to the ERG25 gene from Saccharomyces cerevisiae which encodes the sterol-4alpha-methyl oxidase (SMO), a membrane-bound non-heme di-iron oxygenase involved in lipid metabolism. Heterologous expression of AtSMO1 and AtSMO2 in a yeast erg25 ergosterol auxotroph, lacking SMO activity, restored growth and endogenous ergosterol synthesis. These results represent the first functional identification of SMO genes from plants.