Expression analysis of biosynthetic genes of thymol and carvacrol in different tissues of thyme (Thymus vulgaris)

Thymus vulgaris is one of the most important medicinal plants with more than 20 types of known important chemical compositions. A gene named 1-deoxy-d-xylulose 5-phosphate reductoisomerase (DXR) acts as an important control point, as this is the first committed step in the MEP pathway. γ-terpinene is a key component in essential oil of thyme which constituted up to 30% of the essential oil in the species and is biosynthesized via γ-terpinene as a penultimate precursor. Different cytochrome P450 including CYP71D178 and CYP71D182 are involved in the biosynthesis of thymol and carvacrol in thyme and oregano via the γ-terpinene as an intermediate. The aim of the present work was to study the expression patterns of genes involved in thymol and carvacrol biosynthesis including DXR, γ-terpinene synthase, CYP71D178 and CYP71D180 genes in flowers and leaves of thyme. Gene expression analysis of DXR, γ-terpinene synthase, CYP71D178 and CYP71D180 genes were carried out by semi-quantitative RT-PCR technique. The relative gene expression of flowers compared with leaves for DXR, γ-terpinene synthase, CYP71D178 and CYP71D180 genes were 1.7, 2.7, 1.9 and 2 fold higher, respectively and the gene expression intensity varied for each gene. Expression of aforementioned genes in glandular trichomes were high, hence the higher gene expression in flowers might be related to higher density of glandular trichomes. Based on these results, higher content of essential oils in flowers compared to leaves is most likely further related to the higher expression of related genes in flowers rather than leaves.