State Key Laboratory of Crop Stress Biology for Arid Areas, College of Horticulture, Northwest A&F University, Yangling, 712100, Shaanxi, PR China.
College of Forestry, Henan University of Science and Technology, Luoyang, 471023, Henan, PR China.
Plant Sci. 2021 Feb;303:110761. doi: 10.1016/j.plantsci.2020.110761. Epub 2020 Nov 17.
Seed germination is a vital stage in the plant life-cycle that greatly contributes to plant establishment. Melatonin has been shown to promote seed germination under various environmental stresses; however, the mechanism remains largely underexplored. Here, we reported that melatonin antagonized abscisic acid (ABA) to promote seed germination by regulating ABA and gibberellic acid (GA) balance. Transcriptomic analysis revealed that such a role of melatonin was associated with Ca and redox signaling. Melatonin pretreatment induced Ca efflux accompanied by an up-regulation of vacuolar H+/Ca antiporter 3 (CAX3). AtCAX3 deletion in Arabidopsis exhibited reduced Ca efflux. Inhibition of Ca efflux in the seeds of melon and Arabidopsis mutant AtCAX3 compromised melatonin-induced germination under ABA stress. Melatonin increased HO accumulation, and HO pretreatment decreased ABA/GA ratio and promoted seed germination under ABA stress. However, complete inhibition of HO accumulation abolished melatonin-induced ABA and GA balance and seed germination. Our study reveals a novel regulatory mechanism in which melatonin counteracts ABA to induce seed germination that essentially involves CAX3-mediated Ca efflux and HO accumulation, which, in turn, regulate ABA and GA balance by promoting ABA catabolism and/or GA biosynthesis.
种子萌发是植物生命周期中的一个关键阶段，对植物的建立有很大的贡献。褪黑素已被证明能在各种环境胁迫下促进种子萌发；然而，其机制在很大程度上仍未得到充分探索。在这里，我们报道褪黑素通过调节脱落酸（ABA）和赤霉素（GA）的平衡来拮抗脱落酸（ABA）以促进种子萌发。转录组分析表明，褪黑素的这种作用与 Ca 和氧化还原信号有关。褪黑素预处理诱导 Ca 外流，并上调液泡 H+/Ca 反向转运蛋白 3（CAX3）。拟南芥中 AtCAX3 的缺失表现出 Ca 外流减少。在甜瓜和拟南芥突变体 AtCAX3 的种子中抑制 Ca 外流，会损害褪黑素在 ABA 胁迫下诱导的萌发。褪黑素增加了 HO 的积累，HO 预处理降低了 ABA/GA 比值，并促进了 ABA 胁迫下的种子萌发。然而，完全抑制 HO 的积累会破坏褪黑素诱导的 ABA 和 GA 平衡以及种子萌发。我们的研究揭示了一种新的调控机制，褪黑素拮抗 ABA 诱导种子萌发，其本质上涉及 CAX3 介导的 Ca 外流和 HO 的积累，进而通过促进 ABA 分解代谢和/或 GA 生物合成来调节 ABA 和 GA 的平衡。
