The Expression of Limonene Biosynthesis Pathway Key Genes under Drought Stress in Dracocephalum kotschyi at Vegetative and Flowering Stages

 Dracocephalum kotschyi is an endemic medicinal plant in Iran belonging to the Lamiaceae family. One of the most important monoterpenes identified in this plant is limonene. Drought stress is one of the factors affecting the content of monoterpene in medicinal plants.  In this study, the effect of different levels of drought stress was investigated on the expression of some genes involved in limonene biosynthetic pathway in D. kotschyi at two growth stages.
 

 This experiment was conducted as a factorial experiment with two factor included drought stress and growth stages in a completely randomized design with three replications. Drought stress consisted of severe (25% FC), moderate (50% FC), low (75% FC) stress and non-stress or control (100% FC) and growth stages consisted of vegetative and flowering. Secondary metabolites were analyzed and the amount of limonene was measured by GC / MS using Head-space method and the relative expression of key genes involved in limonene biosynthesis was measured using Real Time PCR.
 

 Analysis of secondary metabolites showed, one of the main monoterpenes was limonene whose amounts was 20.57 % and 13.41% during vegetative and flowering stages, respectively. Drought stress significantly increased HMGR and DXS gene expression during flowering stage, while during vegetative stage no significant change was observed on expression of both genes. In both growth stages, low drought stress increased HDR gene expression, although at flowering stage this increase was not significant but severe drought decreased HDR gene expression, although this decrease was not significant at vegetative stage. Drought stress decreased LS gene expression during flowering stage and increased it during vegetative stage.
 

 The results indicated that limonene content and expression of limonene biosynthesis key genes in D. kotschyi under drought stress are growth stage-specific.