Effects of methyl jasmonate and chitosan nanoparticle treatments on field-grown hemp inflorescences: Integrating transcriptomic and secondary metabolite insights

Industrial hemp (Cannabis sativa L.) is valued for its industrial, food, medical and recreational applications due to its bioactive secondary metabolites, including phenols, cannabinoids and terpenes, which accumulate at low concentrations (<1 % dry weight) in female inflorescences and increase under stress. This study aimed to enhance these compounds by applying methyl jasmonate (MeJA), either alone or encapsulated in chitosan nanoparticles, to female plants of the dioecious cultivar Tiborszallasi grown under field conditions. Treatments included 1 mM and 10 mM MeJA, chitosan nanoparticles (CHT) alone and nanoparticles loaded with 1 mM MeJA. Inflorescences were sampled at early and mature developmental stages, at two time-points per stage: 6 h and 6 days post-treatment. Overall, treatment with 10 mM MeJA significantly increased phenols (+21.2 %), flavonoids (+49.5 %), antioxidant activity (+43.7 %), CBDA (+78.4 %) and terpenes (+94.7 %) in mature inflorescences harvested 6 days after treatment. RNA-Seq analysis scored MeJA marker responses and revealed dose-dependent transcriptional changes. Weighted correlation network and gene co-expression network analyses revealed key regulatory and metabolic genes associated with secondary metabolism, including cannabinoid, phenylpropanoid and terpene pathways. These analyses underscored the central role of the fatty acid biosynthetic pathway in cannabinoid accumulation and highlighted a TALE- and SQUAMOSA-driven transcriptional network as pivotal in the developmental transition from meristem-rich to highly differentiated inflorescences specialized in secondary metabolite production. Overall, this study provides insights into MeJA elicitation of secondary metabolism and identifies regulatory hubs and candidates not previously associated with secondary metabolism in Cannabis sativa for enhancing the therapeutic and commercial potential of industrial hemp.