Oregano or marjoram? The enzyme γ-terpinene synthase affects chemotype formation in the genus Origanum

The enzyme γ-terpinene synthase has a key position in the biosynthesis of essential oil compounds in the genus Origanum. It catalyses the cyclization of GPP to γ-terpinene giving rise to the "cymyl";-pathway and the accumulation of γ-terpinene, p-cymene, carvacrol, and related compounds in a plant. A comprehensive sequence analysis of a part of the γ-terpinene synthase gene (intron 2, exon 3, and intron 3) in O. dubium, O. majorana, O. onites, O. syriacum (section Majorana), and O. vulgare (section Origanum) revealed six different variants of the gene that were distinguishable according to sequence characteristics in intron 3. The formation of "cymyl";-compounds was found to be associated with the presence of variants 1 and/or 3 and/or 4 of the γ-terpinene synthase gene. In plants lacking these gene variants "cymyl";-compounds were completely absent or present in trace amounts only. The alternative "sabinyl";-chemotype (O. majorana) as well as the linalool-chemotype (Turkish O. dubium and O. onites) could...