Expression analysis of the key genes involved in Biosynthesis Pathway of Carvacrol in Satureja mutica fisch & CA mey under Drought Stress

Medicinal plants have long been recognized as a rich source of essential oils and have been cultivated for a variety of uses since ancient times. White savory (Satureja mutica fisch & CA mey) is one of the medicinal plants belonging to the mint family with high content of carvacrol in its essential oil. A large body of literature has suggested that abiotic stresses, especially drought stress, could considerably boost the production of essential oils in plants. The aim of this study was to evaluate the effect of drought stress on the expression of genes affecting the biosynthesis of the main component of white savory essential oil carvacrol.

For this goal, a number of 20 pot-planted seedlings of white savory at the 6-8 leaf stage were subjected in a greenhouse to two conditions of control and drought stress (10 pots for each condition) with irrigation regimes of 100% and 30% of field capacity, respectively. In order to ensure the implementation of stress on plants and to determine the appropriate time for sampling, leaf proline and relative water content of plants were measured.

The results of both proline and relative water content tests revealed a significant statistical difference between the control and stress conditions in white savory at 30% of field capacity. The KEGG (Kyoto Encyclopedia of Genes and Genomes) database was used to obtain information on carvacrol biosynthesis pathway. The three key genes geranyl diphosphate synthase (gpps), terpene synthase (tps), and limonene hydroxylase (lh) were chosen for gene expression analysis. Due to the lack of genomic information on white savory, the sequence information of the genes in the closest genera within the family mint was used to design primers. The result of melting curve analysis from the real-time quantitative PCR (qPCR) assay confirmed the accuracy of the primer design. The raw qPCR data normalized to the housekeeping gene Actin, then differential expression analysis was preformed using the delta delta Ct method. qPCR result showed that expression of the genes gpps, tps, and lh were increased in stressed plants proximately 20, 18, 50 times, compared to those in control, respectively. 

The conclusion that must be drawn from the data available is that water stress leads to the process of plant response to stress and changes the expression of genes involved in the biosynthesis pathway of the active substance carvacrol.