mRNA sequencing revealed transcriptional variability of terpene and eugenol synthase genes among distinct oil yielding accessions of Ocimum sanctum L.

Ocimum sanctum one of the important medicinal plants, lacking adequate molecular resources. In this study, whole mRNA sequencing was carried out towards development of molecular resources, especially correlating with terpenoid biosynthesis and expression of such genes in high and low oil yielding accessions of O. sanctum. The transcriptome sequencing resulted 333.91 and 373.10 million high-quality reads in OS1 and OS38 respectively. In OS1 out of 31,820 transcripts, 30,217 transcripts were annotated and in OS38 out of 32,564 transcripts total 30546 transcripts were annotated. KEGG pathway analysis identified 25,643 transcripts in OS1 and 26,382 in OS38. GO and KEGG annotations enabled the identification of trait-specific genes, including those involved in terpenoid biosynthesis. These findings were supported by GC-MS analysis, which showed the presence of 33 terpenoid compounds in the essential oils. Further, relative expression analysis of six genes responsible for terpenoid and eugenol biosynthesis were performed using RT-PCR to confirm transcript presence. Germacrene A Synthase in OS1 and 3 S Linalool Synthase in OS38 showed higher expression as compared to other genes. RT-PCR results were interpreted as qualitative expressions. These results provide scientific insights into transcript diversity of terpenoid biosynthesis and serve as a basis for future genetic improvement of O. sanctum.