Elicitation effects of methyl jasmonate on iridoid biosynthesis in leaves of Nepeta rtanjensis and Nepeta nervosa

Abstract

The genus Nepeta L. comprises medicinal plant species that synthetize terpenes and phenolics of therapeutic value. Considerable variability in qualitative and quantitative content of iridoid monoterpenoids has been detected within the genus Nepeta, which comprises iridoid produc-ing and non-producing species. Nepeta rtanjensis Diklić & Milojević is an endemic plant of the Balkan Peninsula, which produces both iridoid aglycones (IAs) and iridoid glucosides (IGs). N. nervosa Royle ex Benth., endemic to the Himalayas of Kashmir, India, and Paki-stan, is iridoid-lacking species. This study aimed to comparatively analyze the effect of me-thyl jasmonate (MeJA), an elicitor of terpene production in many plant species, on iridoid bio-synthesis at the molecular level. Iridoid content in MeJA-treated N. rtanjensis and N. nervosa plants under in vitro conditions was analysed in parallel with the co-expression patterns of iridoid related biosynthetic genes (GPPS, GES, G80, 8HGO, 7DLGT, IS, and NEPS), major latex protein-like gene (MLPL), and genes coding for different transcription factors (MYC2, YABBY5, COI1, and JAZ3). In general, the exogenous application of 250 µM MeJA for 2 h, 24 h and 72 h resulted in an increased accumulation of targeted IAs (trans, cis-nepetalactone and 5,9-dehydronepetalactone) and IGs (1,5,9-epideoxyloganic acid) in leaves of N. rtanjensis, as a result of elevated expression of the key biosynthetic genes. Interestingly, although the majority of iridoid-related biosynthetic genes and TFs were identified in transcriptome of N. nervosa leaves, and the expression of some of them (NEPS and JAZ3) is up-regulated follow-ing MeJA treatment, no iridoids were accumulated in leaves of N. nervosa.