Physiological and Transcriptomic Insights Into the Regulatory Effects of Methyl Jasmonate on Growth and Bioactive...

Methyl jasmonate (MeJA) is a key plant growth regulator that influences growth and medicinal compound accumulation in Dendrobium nobile. This study investigated the effects of different MeJA concentrations (0, 100, 200, 400, and 800 μmol l^-1) and identified 200 μmol l^-1 as the optimal concentration for significantly enhancing growth, physiological traits, and bioactive compound synthesis after a 28-day treatment. The 200 μmol l^-1 MeJA treatment markedly improved plant height, stem diameter, leaf size, and photosynthetic pigment content. It also boosted antioxidant enzyme activities while reducing malondialdehyde levels and increasing osmolyte content. Furthermore, this treatment significantly elevated the accumulation of polysaccharides, total flavonoids, and polyphenols. MeJA treatment was associated with altered expression of MYC2 and JAZ, suggesting possible activation of JA signaling, concurrently promoting the expression of key genes involved in flavonoid and polyphenol biosynthesis, such as CHS, CHI, and 4CL. qRT-PCR validation of 12 differentially expressed genes (DEGs) showed strong concordance with the transcriptomic data. The validated DEGs included key genes involved in phenylpropanoid/flavonoid biosynthesis (CYP73A, HCT, COMT, UBC, and CHI), plant hormone signal transduction (JAZ, PYL, PP2C, and GH3) and plant-pathogen interaction (CALM, RIN4, and CPK). These results suggest that 200 μmol l^-1 MeJA may enhance both the medicinal quality and stress adaptation of D. nobile, providing insights for the targeted application of phytohormones in its cultivation.