December 2024
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Melatonin Research
Serotonin N-acetyltransferase (SNAT) is the penultimate enzyme catalyzing serotonin into N-acetylserotonin in the melatonin biosynthetic pathway. Recently, an archaeal SNAT from Thermoplasma volcanium (TvSNAT) was cloned and rice lines with its ectopic overexpression (TvSNAT-OE) exhibited higher melatonin levels and generated larger seeds than those of the wild type (WT). In this study, we hypothesized that the increased seed size in TvSNAT-OE rice line might be linked to enhanced brassinosteroid (BR) synthesis since melatonin level is positively associated with BR production. In rice seedlings, roots were shorter and the lamina angle was larger in TvSNAT-OE lines than those in the WT. Also, the second leaves of seedlings were longer in the TvSNAT-OE lines than that in the WT, supporting BR elevation in the TvSNAT-OE lines. In parallel with these phenotypic features, BR levels were higher in the TvSNAT-OE lines than that in the WT. Increased BR levels were associated with enhanced expression of DWARF4 and BZR1, the key genes for BR biosynthesis and signaling, in the TvSNAT-OE lines compared with the WT. Consequently, the TvSNAT-OE lines showed delayed senescence, but were more susceptible to salt stress than the WT due to enhanced BR levels.