The effect of drought stress on the expression of some genes involved in monoterpene and sesquiterpanes biosynthesis and essential oil compounds in basil

Background: Basil (Ocimum basillicum L.) is one of the most important medicinal plants belong to Lamiaceae family. Basil essential oil contains important terpenoid compounds, including monoterpanes and sesquiterpanes widely used in drug industries. Objective: In the current investigation, a completely randomized design-based experiment was conducted in greenhouse with three replications and treatments to study the effect of drought stress on the expression of some genes involved in monoterpanes and sesquiterpenes biosynthesis including selinene synthase (SES), beta-myrcene synthase (MYS), gamma-cadinene synthase (CDS), alpha-zingeberene synthase (ZIS) and geraniol synthase (GES), and the compounds produced by these genes in O. basilicum c.v. Keshkeni luvelou. Methods: Drought stress was applied at three levels of 100, 75 and 50% of field capacity (FC) at 6-8 leaf stages. Results: Analysis of gene expression data revealed that treatments 75% and 50% of FC increase the GES expression two and 3.8 times, MYS expression 16 and 17.4 times, and expression of the ZIS 1.31 and 1.41 times, respectively. The expression of SES gene was almost constant and the CDS expression was declined. Conclusion: the results of essential oil analysis showed that drought stress reduced the geraniol content, but increased beta-myrcene and gamma-cadinene contents. The results also showed that changes in MYS expression was consistent with the beta-myrcene content under drought stress conditions.