Cell Wall Extract from Piriformospora indica Enhances Valerenic Acid Content in Valerian Roots via Modulating Sesquiterpene Synthase Genes

Valerenic acid (VA) as a sesquiterpene constituent responsible for medicinal properties is derived from valerian (Valeriana officinalis). It is well documented that the mutualistic basidiomycete Piriformospora indica substantially promotes secondary metabolites production. Nevertheless, our knowledge about the molecular mechanism involved is rudimentary. In this study, we aimed to find the effect of P. indica cell wall extract (CWE) in the modulation of the transcriptional rate of sesquiterpene synthase (Sesqui-TPS) genes involved in VA biosynthesis in the host plant, V. officinalis. For this purpose, relative expression of putative terpene syntheses (VoTPS1, VoTPS3 and VoTPS7) genes was quantified by quantitative realtime PCR in the roots of valerian plants inoculated by two concentrations of the extract (2 and 4 % v/v) prepared from the cell wall of P. indica for various time intervals. As well as, VA content of roots of V. officinalis was measured. According to the results, The 4% fungal CWE application produced more VA than 2% CWE treated plants at the exposure time of 72 h. Such enhancement was correlated with increased transcript expression of two sesquiterpene synthases (sesqui-TPSs) including VoTPS1 and VoTPS7 which provided intermediates probably serving in the VA-biosynthetic pathway, while different expression pattern of VoTPS3 showed that it probably has no influence on the biosynthesis of VA. Since the accumulation of VA is a dose (and time) dependent response at roots of V. officinalis, the present study suggests that the mechanism(s) responsible for the enhancement of VA could be related to the fungus-plant association.