Melatonin is a well-studied neurohormone oscillating in a 24-h cycle in vertebrates. Phytomelatonin is widespread in plant kingdom, but it remains elusive whether this newly characterized putative hormone underlies the regulation by daily rhythms. Here, we report phytomelatonin signaling, as reflected by changes in endogenous concentrations of phytomelatonin and expression of genes associated with biosynthesis of phytomelatonin (AtSNAT1, AtCOMT1, and AtASMT) and its receptor (AtPMTR1), shows 24-h oscillations in Arabidopsis. The variation of reactive oxygen species (ROS) production and scavenging and expression of ROS-related genes significantly decrease in pmtr1 and snat and increase in PMTR1-OE seedlings, indicating the rhythmicity in phytomelatonin signaling is required for maintenance of ROS dynamics. Additionally, the ROS signaling feedback influences the expression of AtSNAT1, AtCOMT1, AtASMT, and AtPMTR1, suggesting the phytomelatonin and ROS signaling are coordinately interrelated. The pmtr1 mutant plants lose diurnal stomatal closure, with stomata remaining open during daytime as well as nighttime and mutants showing more water loss and drought sensitivity when compared with the wild-type Col-0 plants. Taken together, our results suggest that PMTR1-regulated ROS signaling peaks in the afternoon and may transmit the darkness signals to trigger stomatal closure, which might be essential for high water-use efficiency and drought tolerance.

中文翻译：

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褪黑素信号转导的日常节律通过调节拟南芥中的活性氧物种动态来调节昼夜气孔关闭。

褪黑激素是在脊椎动物中以24小时周期振荡的经过充分研究的神经激素。植鞣素在植物界很普遍，但是这种新表征的推定激素是否能以日常节律为基础尚不清楚。在这里，我们报道了植物降钙素信号传导，反映在植物激素的内源性浓度变化以及与植物降钙素（AtSNAT1，AtCOMT1和AtASMT）及其受体（AtPMTR1）的生物合成相关的基因的表达中，显示了拟南芥中的24小时振荡。在pmtr1和snat中，活性氧（ROS）的产生，清除和ROS相关基因的表达显着降低，而PMTR1-OE幼苗则增加，这表明维持植物ROS动态需要植物褪黑素信号的节律性。另外，ROS信号反馈影响AtSNAT1，AtCOMT1，AtASMT和AtPMTR1的表达，这表明植物降钙素和ROS信号相互协调。与野生型Col-0植物相比，pmtr1突变植物失去昼夜气孔关闭功能，白天和夜间的气孔均保持开放，并且突变体显示出更多的水分流失和干旱敏感性。两者合计，我们的结果表明，PMTR1调节的ROS信号在下午达到峰值，并可能传输暗信号以触发气孔关闭，这可能对高用水效率和干旱耐受性至关重要。与野生型Col-0植物相比，白天和晚上的气孔在白天和晚上都保持开放状态，并且突变体显示出更多的水分流失和干旱敏感性。两者合计，我们的结果表明，PMTR1调节的ROS信号在下午达到峰值，并可能传输暗信号以触发气孔关闭，这可能对高用水效率和干旱耐受性至关重要。与野生型Col-0植物相比，白天和晚上的气孔在白天和晚上都保持开放状态，并且突变体显示出更多的水分流失和干旱敏感性。两者合计，我们的结果表明，PMTR1调节的ROS信号在下午达到峰值，并可能传输暗信号以触发气孔关闭，这可能对高用水效率和干旱耐受性至关重要。