Molecular cloning, expression and characterization of drought responsive promoter of linalool synthase gene (Lins) in some populations of basil (Ocimum basilicum L.)

Basil (Ocimum basilicum L.) is a medicinal and aromatic plant, which is used in traditional Iranian medicine. Monoterpenes, sesquiterpenes and phenylpropanoids make up the bulk of the essential oil of basil. A significant part of terpenoids is composed of the volatile monoterpene compound linalool, which is very important in the plant's tolerance mechanism against various environmental stresses due to its defensive effects. Linalool synthase (Lins), as a key enzyme of terpenoids biosynthesis pathway, converts the main precursor of monoterpenes into final compound linalool. In current research, to explore the formation and transcriptional control exerted on this pathway, relative expression profile of key gene in the biosynthesis pathway of linalool (ObLins) were evaluated in the three cultivars of O. basilicum under control (100% FC) and the three levels of drought stress (W1: 75% FC, W2: 50% FC and W3: 25% FC) using quantitative real-time PCR. In order to regulate the expression pattern of ObLins gene under drought stress, isolation, characterization and functional analysis of pObLins promoter were performed. The results show that in the promoter of this gene, regulatory elements responsive to drought stress including MBS, MYB-site, WRKY710S, W-Box, CCAAT-Box, DRE2 and CBFHV and the binding site of transcription factors influencing gene transcription of linalool synthase is present under drought stress. Transient expression of the GUS gene under pObLins promoter control in Nicotiana tabacum leaves showed that this promoter with the presence of core elements was able to direct the basal expression of this gene. Due to the presence of cis-regulatory elements responding to biotic and abiotic stresses in the ObLins gene promoter, it is expected that this promoter will be able to express the ObLins gene in response to environmental stresses by regulating its transcription rate.