Genome-Wide Identification and Functional Characterization of New Serotonin N-Acetyltransferases in Soybean

Melatonin is recognized as a crucial plant hormone due to its significant role in plant development, growth promotion, enhancing antioxidant activity, and stress resistance. Soybean is one of the most important crops globally. To date, three SNAT genes have been cloned in Arabidopsis and rice; however, only one gene, GmSNAT1, has been characterized in soybeans. In this study, members of the GmGNAT family were identified through genome-wide analysis. Two candidate GmSNAT genes (GmSNAT3.1 and GmSNAT3.2) were selected based on phylogenetic tree analysis and exhibited highly similar protein tertiary structures to ZmSNAT3. Furthermore, the functionality of these two GmSNAT genes was confirmed for synthesizing N-acetylserotonin or melatonin using serotonin or 5-methoxytryptamine as substrates in vitro. RNA-seq data indicated that the transcription levels of GmSNAT3.1 and GmSNAT3.2 were downregulated under conditions of dehydration and salt stress. Additionally, SNAT3 genes from other leguminous plants were identified through homology analysis with GmSNAT genes. This study elucidates the role of SNAT genes in soybeans and establishes a foundation for further exploration into the physiological functions of melatonin within legume plants.