Tissue-specific expression of PAL and RAS genes in response to melatonin and UV-C elicitation in Dracocephalum kotschyi under in vitro conditions
摘要
Dracocephalum kotschyi Boiss. is an endemic and endangered medicinal plant of Iran, valued for its phenylpropanoid-derived compounds. Due to extensive wild harvesting, the development of in vitro approaches for conservation and physiological assessment of this species has gained increasing attention. In the present study, an in vitro culture system was established to evaluate the effects of melatonin and UV-C radiation, individually and in combination, on the expression of two key genes involved in the phenylpropanoid pathway, phenylalanine ammonia-lyase (PAL) and rosmarinic acid synthase (RAS), in callus and plantlet tissues of D. kotschyi. Leaf explants were cultured on Murashige and Skoog (MS) medium to induce callus and plantlet formation, followed by treatments with melatonin (0, 10, 15, and 20 µmol L−1) and UV-C radiation (0, 2.5, 5, and 9.5 kJ m−2) arranged in a factorial experimental design. Gene expression levels were quantified using real-time quantitative PCR (qPCR). Both melatonin and UV-C treatments significantly affected PAL and RAS transcript levels (p ≤ 0.01), with responses depending on elicitor dose, tissue type, and their interaction effects. PAL expression was strongly induced in callus tissues, reaching its maximum at 10 µmol L−1 melatonin and 5 kJ m−2 UV-C, while plantlets showed a distinct interaction-dependent response under combined treatments. In contrast, RAS expression was most responsive to melatonin treatment, peaking at 15 µmol L−1, particularly in callus cultures, while UV-C-induced expression was more pronounced in plantlet tissues. Comparison between treated samples and untreated controls indicated that the induction of PAL and RAS was clearly elicitor-dependent, as no significant expression changes were observed in the control groups. Overall, these results demonstrate that melatonin and UV-C radiation modulate PAL and RAS gene expression in a tissue-specific and interaction-dependent manner under in vitro conditions. The study provides molecular-level insights into elicitor-responsive regulation of phenylpropanoid pathway genes in D. kotschyi, contributing to a better understanding of interaction-dependent transcriptional responses in this endangered medicinal species.