Molecular responses of watermelon seedlings to MgO nanoparticles: transcriptome and metabolome insights

MgO nanoparticles (MgO NPs) exhibit considerable potential in regulating plant development. This study firstly demonstrates that MgO NPs at 100-200 mg/L enhance the growth of watermelon (Citrullus lanatus) seedlings, resulting in 18.7-32.8 % and 23.8-46.5 % increases in the over ground fresh and dry weights, respectively. Significant changes in the accumulation of multiple metabolites were identified after MgO NPs treatment, such as carboxylic acids and derivatives, benzene and substituted derivatives, fatty acyls, and organooxygen compounds. MgO NPs enhance watermelon growth primarily by upregulating pathways involved in photosynthesis, carbohydrate metabolism, and energy metabolism. Key genes rbcL, INV, and GOLS, and metabolites oxoglutaric acid and glyceric acid were significantly elevated. Furthermore, MgO NPs exhibited significant potential to strengthen resistance of watermelon seedling by activating plant hormone-mediated signal transduction, phenylpropanoid biosynthesis and secondary metabolite biosynthesis pathways, and as evidenced by increased expression PR1, LOX1_5 and PAL genes and accumulation of jasmonic acid (JA) and metabolites related to stress tolerance, such as caffeate, isovitexin, and isovitexin 2″-O-beta-D-glucoside. These findings elucidate the molecular mechanisms through which MgO NPs enhance watermelon growth and development, highlighting the potential practical application of nano-fertilizers in watermelon cultivation.