Seed oils of a number of Asteraceae and Euphorbiaceae species are enriched in 12-epoxyoctadeca-cis-9-enoic acid (vernolic acid), an unusual 18-carbon Δ12-epoxy fatty acid with potential industrial value. It has been previously demonstrated that the epoxy group of vernolic acid is synthesized by the activity of a Δ12-oleic acid desaturase-like enzyme in seeds of the Asteraceae Crepis palaestina and Vernonia galamensis. In contrast, results from metabolic studies have suggested the involvement of a cytochrome P450 enzyme in vernolic acid synthesis in seeds of the Euphorbiaceae species Euphorbia lagascae. To clarify the biosynthetic origin of vernolic acid in E. lagascae seed, an expressed sequence tag analysis was conducted. Among 1,006 randomly sequenced cDNAs from developing E. lagascae seeds, two identical expressed sequence tags were identified that encode a cytochrome P450 enzyme classified as CYP726A1. Consistent with the seed-specific occurrence of vernolic acid in E. lagascae, mRNA corresponding to the CYP726A1 gene was abundant in developing seeds, but was not detected in leaves. In addition, expression of the E. lagascae CYP726A1 cDNA in Saccharomyces cerevisiae was accompanied by production of vernolic acid in cultures supplied with linoleic acid and an epoxy fatty acid tentatively identified as 12-epoxyoctadeca-9,15-dienoic acid (12-epoxy-18:2Δ9,15) in cultures supplied with α-linolenic acid. Consistent with this, expression of CYP726A1 in transgenic tobacco (Nicotiana tabacum) callus or somatic soybean (Glycine max) embryos resulted in the accumulation of vernolic acid and 12-epoxy-18:2Δ9,15. Overall, these results conclusively demonstrate that Asteraceae species and the Euphorbiaceae E. lagascae have evolved structurally unrelated enzymes to generate the Δ12-epoxy group of vernolic acid.
ASJC Scopus subject areas
- Plant Science