The effect of drought stress on the expression of genes encoding phenylalanine ammonia lyase (PAL), eugenol synthase 1 (EGS1) and caffeic acid O-methyltransferase (COMT) enzymes in Basil (Ocimum basilicum)

Basil (Ocimum basilicum L.) is one of the important medicinal plants belonging to the mint family which is a rich source of phenylpropanoid compounds such as methylchavicol and methyleugenol. Environmental stresses such as drought could change the percentage and content of the essential oils and expression level of the genes involved in their biosynthesis. In the current study, an experiment based on completely randomized design (CRD) with three replications was conducted in greenhouse to study the effect of drought stress on the expression of key genes involved in phenylpropanoids biosynthesis in O. basilicum c.v. Keshkeni luvelou. The genes studied, were phenylalanine ammonialyase (PAL), eugenol synthase 1 (EGS1) and caffeic acid O-methyltransferase (COMT). Plants were exposed to three levels of 100 (control), 75 and 50 % field capacity (FC) at the 6-8 leaf stage. The expression level of the studied genes were determined by real time PCR technique in plant leaves at the flowering stage. Analysis of gene expression data indicated that 50% FC increases the expression level of EGS1 by about 9.74, whereas those of COMT relatively remained unchanged. The expression level of PAL was increased 1.5 to 2 times under drought stress, although no significant difference for its expression was observed between 50% and 75% FC. Thus, it is possible to enhance the content of the phenylpropanoid compounds in basil through the application of controlled drought stress and consequently increasing the expression levels of EGS1 and PAL genes.