College of Horticulture, China Agricultural University, Beijing, China.
College of Biological Sciences, China Agricultural University, Beijing, China.
J Exp Bot. 2022 Aug 11;73(14):4941-4953. doi: 10.1093/jxb/erac176.
Melatonin (N-acetyl-5-methoxytryptamine) biosynthesis in plants is induced by darkness and high-intensity light; however, the underlying transcriptional mechanisms and upstream signalling pathways are unknown. We identified a dark-induced and highly expressed melatonin synthetase in Arabidopsis thaliana, AtSNAT6, encoding serotonin N-acetyltransferase. We assessed melatonin content and AtSNAT6 expression in mutants lacking key regulators of light/dark signalling. AtCOP1 (CONSTITUTIVE PHOTOMORPHOGENIC 1) and AtHY5 (ELONGATED HYPOCOTYL 5), which control light/dark transition and photomorphogenesis, promoted and suppressed melatonin biosynthesis, respectively. Using EMSA and ChIP-qPCR analysis, we showed that AtHY5 inhibits AtSNAT6 expression directly. An analysis of melatonin content in snat6 hy5 double mutant and AtHY5+AtSNAT6-overexpressing plants confirmed the regulatory function of AtHY5 and AtSNAT6 in melatonin biosynthesis. Exogenous melatonin further inhibited cotyledon opening in hy5 mutant and AtSNAT6-overexpressing seedlings, but partially reversed the promotion of cotyledon opening in AtHY5-overexpressing seedlings and snat6. Additionally, CRISPR/Cas9-mediated mutation of AtSNAT6 increased cotyledon opening in hy5 mutant, and overexpression of AtSNAT6 decreased cotyledon opening in AtHY5-overexpressing seedlings via changing melatonin biosynthesis, confirming that AtHY5 decreased melatonin-mediated inhibition of cotyledon opening. Our data provide new insights into the regulation of melatonin biosynthesis and its function in cotyledon opening.
植物中的褪黑素（N-乙酰-5-甲氧基色胺）生物合成受黑暗和高强度光照诱导；然而，其潜在的转录机制和上游信号通路尚不清楚。我们在拟南芥中鉴定出一种黑暗诱导的、高度表达的褪黑素合成酶 AtSNAT6，它编码 5-羟色胺 N-乙酰转移酶。我们评估了缺乏光/暗信号关键调节因子的突变体中的褪黑素含量和 AtSNAT6 表达。AtCOP1（CONSTITUTIVE PHOTOMORPHOGENIC 1）和 AtHY5（ELONGATED HYPOCOTYL 5）分别控制光/暗转换和光形态发生，促进和抑制褪黑素生物合成。通过 EMSA 和 ChIP-qPCR 分析，我们表明 AtHY5 直接抑制 AtSNAT6 的表达。snat6 hy5 双突变体和 AtHY5+AtSNAT6 过表达植物中褪黑素含量的分析证实了 AtHY5 和 AtSNAT6 在褪黑素生物合成中的调节作用。外源褪黑素进一步抑制了 hy5 突变体和 AtSNAT6 过表达幼苗的子叶张开，但部分逆转了 AtHY5 过表达幼苗和 snat6 中对子叶张开的促进作用。此外，CRISPR/Cas9 介导的 AtSNAT6 突变增加了 hy5 突变体中的子叶张开，而 AtHY5 过表达幼苗中 AtSNAT6 的过表达通过改变褪黑素生物合成降低了子叶张开，证实了 AtHY5 降低了褪黑素介导的对子叶张开的抑制作用。我们的数据为褪黑素生物合成的调控及其在子叶张开中的作用提供了新的见解。
