Transcriptional Response of Structural and Regulatory Genes Involved in Isoprene Biosynthesis and its Relation to Essential Oil Biosynthesis in Response to Salicylic Acid and Abscisic Acid in Mentha piperita L.

In peppermint, precursors for the biosynthesis of monoterpenes are provided by plastidial methyl-erythritol-phosphate (MEP) pathways.

In order to increase our understanding of terpene metabolism in M. piperita, the effect of salicylic acid (SA) and abscisic acid (ABA) in the modulation of expression pattern of genes involved in essential oil biosynthesis and secretion was investigated.

Transcript abundance of MEP pathway genes, some introduced transcription factors (TFs) families that probably involved in regulating MEP pathway and two genes coding lipid transfer protein (LTP1, LTP2) were monitored by quantitative real time PCR (qRT-PCR) in response to SA and ABA at 12, 24, 48, 72 and 120 h after treatments. As well as, GC/MS was employed to analysis the quality and quantity of essential oil.

In plants treated with SA and ABA, oil yield and menthol content increased. Transcript abundance of MCT and CMK genes increased in response to SA treatment. As well as, ABA treatment substantially enhanced mRNA level of gene encoding HDR and MCT. However, transcript levels of other MEP pathway associated genes were not positively affected by both treatments. Moreover, LTP1 transcript and some trichome activator genes which belong to MYB and C2H2 families were increased. These results suggest that, in addition to the effect of altered isoprene availability on terpenoid biosynthesis, increased quality and quantity of essential oil components in M. piperita upon SA and ABA were mediated by other mechanisms.

These results provide future avenues for investigation of the underlying mechanism of transcriptional regulation of terpenoids to enhance therapeutic efficacy of
M. piperita.