Knockout of <i>Arabidopsis</i> Serotonin <i>N</i>-Acetyltransferase-2 Reduces Melatonin Levels and Delays Flowering
2019
Hyoung Yool Lee | Kyungjin Lee | Kyoungwhan Back
Melatonin plays roles in both plant growth and defense. Serotonin <i>N</i>-acetyltransferase (SNAT) catalyzes formation of <i>N</i>-acetylserotonin (NAS) from serotonin. Plants contain two <i>SNAT</i> isogenes, which exhibit low-level amino acid homology. We studied the <i>Arabidopsis</i> <i>thaliana</i> <i>SNAT2</i> (<i>AtSNAT2</i>) gene; we prepared recombinant SNAT2 protein and characterized a <i>snat2</i> knockout mutant. The SNAT2 protein exhibited 27% amino acid homology with SNAT1; the <i>K</i><sub>m</sub> was 232 μM and the <i>V</i><sub>max</sub> was 2160 pmol/min/mg protein. Melatonin inhibited SNAT enzyme activity in vitro. <i>SNAT2</i> mRNA was abundantly expressed in flowers; the melatonin content of flowers of the <i>snat2</i> mutant was significantly less than that of wild-type flowers. The mutant exhibited delayed flowering and reductions in leaf area and biomass compared to the wild type. Delayed flowering was attributable to reductions in the expression levels of the gibberellin biosynthetic genes <i>ent-kaurene synthase</i> (<i>KS</i>) and <i>FLOWERING LOCUS T</i> (<i>FT</i>).
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