Enhancement of valerenic acid production in Valeriana officinalis roots by methyl jasmonate-mediated transcriptional changes of sesquiterpene synthase genes

Valeriana officinalis (valerian), as a nutraceutical herb, is widely used for its sedative and hypnotic properties. It is known that C15 sesquiterpenoid valerenic acid (VA) is active ingredient responsible for pharmacological effects of V. officinalis. To evaluate the effect of methyl jasmonate (MeJA) concentrations (50 and 100 µM) in the modulation of expression patterns of the genes involved in valerenic acid (VA) biosynthesis, transcript abundance of the identified sesquiterpene synthase (Sesqui-TPS) genes in the root of V. officinalis was monitored by quantitative real time PCR (qRT-PCR) within a 144 h time period. In addition, valerenic acid contents were measured by high-performance liquid chromatography (HPLC). The highest amount of VA (12.45 mg/g dry weight (DW)) was found at 100 µM MeJA with a 12-fold increase over control culture (1.03 mg/g DW) at exposure time of 72 h. Moreover, MeJA in a concentration dependent manner, enhanced transcription rate of VoTPS1 and VoTPS7 genes. Accordingly, exposure to 100 µM MeJA for 24 h can be more effective on induction of these genes than observed for 50 µM. Such enhancement correlated with increased VA accumulation suggesting that these genes may be responsible for the biosynthesis of intermediates involved in the VA-biosynthetic pathway. However, MeJA treatment seemed to have a less significant effect on VoTPS3 expression than VoTPS1 and VoTPS7 genes. These results provide insights for more effective biosynthesis of VA by MeJA-mediated transcriptional changes of putative sesqui-TPS.