Gene expression and metabolite analyses of Thymus daenensis and T.vulgaris in the Trichome and leaf at two phenological stages

Abstract

The trichomes of plant secretions have a rare capacity for chemical synthesis and secretion. Glandular trichomes are responsible for the synthesis, storage, and release of many secondary metabolites such as different types of terpenes. GC–MS analysis showed that thymol, β-caryophyllene, carvacrol, p-cymene, γ-terpinene, borneol, and thymol methyl ether were the major components of T. daenensis and T. vulgaris. Scanning Electron Microscopy identified glandular and non-glandular trichomes distributed on the surfaces of the leaves and stems. In addition, the expression of genes synthesizing various terpene compounds, including thymol and carvacrol, in leaves and trichomes isolated from leaves of T. daenensis and T. vulgaris was evaluated by qPCR at the control (90% field capacity) and drought stress (50% field capacity) moisture levels. CYP71D180 and CYP71D181 genes involved in carvacrol biosynthesis, and CYP71D179/182 gene, which is engaged in thymol biosynthesis, were more expressed in trichomes than in leaves. The highest expression of MVK, TPS4, CYP71D181, CYP71D179/82 (T. vulgaris), and IPP1 (T. daenensis) genes was observed in the 50% flowering stage under control conditions. TPS2 and CYP71D180 showed the highest expression in the vegetative stage of T. vulgaris under drought stress conditions. Most of the gene expression in the 50% flowering stage under drought stress conditions was related to the HDS gene of T. vulgaris. Consequently, it can be stated that peltate glandular trichomes are not only the site of accumulation of monoterpenes but also the site of their biosynthesis.