Exogenous Serotonin and Melatonin Regulate Dietary Isoflavones Profoundly through Ethylene Biosynthesis in Soybean [Glycine max (L.) Merr.].

Serotonin and melatonin are important signaling and stress mitigating molecules. However, their role and molecular mechanism in the accumulation of isoflavones are not clearly defined. To elucidate their functions, serotonin and melatonin were applied to in vitro cultures of soybean at different concentrations and analyzed to assess the accumulation of isoflavone content followed by transcript levels of biosynthesis genes at different time intervals. Increased total phenolics, total flavonoids, and different forms of isoflavone content were observed in the treatments. Expression levels of critical genes in isoflavone, ethylene, jasmonic acid, abscisic acid, and melatonin biosynthesis and related transcription factor were quantified. A correlation was observed between the expression of ethylene biosynthesis genes (S-adenosylmethionine synthase and 1-aminocyclopropane-1-carboxylate oxidase) and isoflavone biosynthesis genes (chalcone synthase, chalcone reductase, and isoflavone synthase). We hypothesize that, under serotonin and melatonin treatments, ethylene biosynthesis may play a role in the increase/decrease in isoflavone content in soybean culture.