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.
N-Acetylserotonin O-methyltransferase (ASMT) is the final enzyme involved in melatonin biosynthesis. Identifying the expression of ASMT will reveal the regulatory role in the development and stress conditions in soybean. To identify and characterize ASMT in soybean (GmASMT), we employed genome-wide analysis, gene structure, cis-acting elements, gene expression, co-expression network analysis, and enzyme assay. We found seven pairs of segmental and tandem duplication pairs among the 44 identified GmASMTs by genome-wide analysis. Notably, co-expression network analysis reported that distinct GmASMTs are involved in various stress response. For example, GmASMT3, GmASMT44, GmASMT17, and GmASMT7 are involved in embryo development, heat, drought, aphid, and soybean cyst nematode infections, respectively. These distinct networks of GmASMTs were associated with transcription factors (NAC, MYB, WRKY, and ERF), stress signalling, isoflavone and secondary metabolites, calcium, and calmodulin proteins involved in stress regulation. Further, GmASMTs demonstrated auxin-like activities by regulating the genes involved in auxin transporter (WAT1 and NRT1/PTR) and auxin-responsive protein during developmental and biotic stress. The current study identified the key regulatory role of GmASMTs during development and stress. Hence GmASMT could be the primary target in genetic engineering for crop improvement under changing environmental conditions.
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