Methyl Jasmonate-Elicited Transcriptional Responses and Pentacyclic Triterpene Biosynthesis in Sweet Basil    

Abstract

Sweet basil (Ocimum basilicum) is well known for its diverse pharmacological properties and has been widely used in traditional medicine for the treatment of various ailments. Although a variety of secondary metabolites with potent biological activities are identified, our understanding of the biosynthetic pathways that produce them has remained largely incomplete. We studied transcriptional changes in sweet basil after methyl jasmonate (MeJA) treatment, which is considered an elicitor of secondary metabolites, and identified 388 candidate MeJA-responsive unique transcripts. Transcript analysis suggests that in addition to controlling its own biosynthesis and stress responses, MeJA up-regulates transcripts of the various secondary metabolic pathways, including terpenoids and phenylpropanoids/flavonoids. Furthermore, combined transcript and metabolite analysis revealed MeJA-induced biosynthesis of the medicinally important ursane-type and oleanane-type pentacyclic triterpenes. Two MeJAresponsive oxidosqualene cyclases (ObAS1 and ObAS2) that encode for 761-and 765-amino acid proteins, respectively, were identified and characterized. Functional expressions of ObAS1 and ObAS2 in Saccharomyces cerevisiae led to the production of b-amyrin and a-amyrin, the direct precursors of oleanane-type and ursane-type pentacyclic triterpenes, respectively. ObAS1 was identified as a b-amyrin synthase, whereas ObAS2 was a mixed amyrin synthase that produced both a-amyrin and b-amyrin but had a product preference for a-amyrin. Moreover, transcript and metabolite analysis shed light on the spatiotemporal regulation of pentacyclic triterpene biosynthesis in sweet basil. Taken together, these results will be helpful in elucidating the secondary metabolic pathways of sweet basil and developing metabolic engineering strategies for enhanced production of pentacyclic triterpenes.

Transcriptome changes in Polygonum multiflorum Thunb. roots induced by methyl jasmonate

“…The concentration of MeJA partially determines whether genes are up-or down-regulated (Sun J.W. et al, 2013;Misra et al, 2014). In our study, some metabolic pathways were characterized by strong down-regulation due to 0.25 mmol/L MeJA.…”

“…3.3.6 Effect of MeJA on the terpenoid biosynthesis pathway Plant terpenoids, which play an important role in the basic life activities of plants, are increased by foliar applications of MeJA (Han et al, 2007;Chang et al, 2013;Misra et al, 2014). We found that genes involved in eight types of terpenoid biosynthesis pathways were induced.…”

“…MeJA participates in the signal transduction pathway that induces particular enzymes to catalyze the formation of low molecular weight defensive compounds in plants (Sivanandhan et al, 2012;Ku and Juvik, 2013;Misra et al, 2014). Production of these compounds, such as alkaloids, terpenoids, and phenylpropanoids, is affected through an extensive transcriptional reprogramming of plant metabolism (Sun G.L.…”

“…The induction of secondary metabolite accumulation is a stress response, which depends on MeJA to coordinate the activation of the expression of multiple biosynthetic genes and the activity of diversifying enzymes (Gaige et al, 2010). MeJA-induced transcriptome changes have been analyzed in many different plant species including wheat and sweet basil (Diallo et al, 2014;Misra et al, 2014).…”

The regulatory mechanism of fungal elicitor-induced secondary metabolite biosynthesis in medical plants

“…ObAS1 was identified as a beta-amyrin synthase, whereas ObAS2 was a mixed amyrin synthase that produced both alpha-amyrin and beta-amyrin but had a product preference for alpha-amyrin. Moreover, transcript and metabolite analysis shed light on the spatiotemporal regulation of pentacyclic triterpene biosynthesis in sweet basil (Misra et al 2014).…”