Genome-wide identification, characterization of Serotonin N-acetyltransferase and deciphering its importance under development, biotic and abiotic stress in soybean.

Serotonin N-acetyltransferase (SNAT) is the penultimate enzyme involved in plant melatonin biosynthesis.
Identifying its expression under development and stress will reveal the regulatory role in the soybean. To identify
and characterize SNAT, we employed genome-wide analysis, gene structure, cis-acting elements, expression, and
enzyme activity. We identified seven putative genes by genome-wide analysis and found chloroplast signal
peptides in three GmSNATs. To elucidate GmSNATs role, expression datasets of more than a hundred samples
related to circadian rhythm, developmental stages, and stress conditions were analysed. Notably, the expression
of GmSNAT1 did not show significant expression during biotic and abiotic stress. The GmSNAT1 sequence
showed 67.8 and 72.2 % similarities with OsSNAT and AtSNAT, respectively. The Km and Vmax of the purified
recombinant GmSNAT1 were 657 μM and 3780 pmol/min/mg, respectively. To further understand the GmSNAT1
role, we supplemented different concentrations of serotonin and melatonin to in-vitro cultures and seed priming.
These studies revealed that the GmSNAT1 expression was significantly up-regulated at higher concentrations of
serotonin and down-regulated at higher melatonin concentrations. We speculate that a high concentration of
melatonin during abiotic, biotic stress, and in-vitro cultures are responsible for regulating GmSNAT1 expression,
which may regulate them at the enzyme level during stress in soybean.