State Key Laboratory of Crop Stress Biology for Arid Areas/Shaanxi Key Laboratory of Apple, College of Horticulture, Northwest A&F University, Yangling, Shaanxi 712100, China.
Tree Physiol. 2022 May 9;42(5):1114-1126. doi: 10.1093/treephys/tpab157.
Improving apple water-use efficiency (WUE) is increasingly desirable in the face of global climate change. Melatonin is a pleiotropic molecule that functions in plant development and stress tolerance. In apple, exogenous application of melatonin has been largely investigated, but melatonin biosynthesis and its physiological roles remain elusive. In the plant biosynthetic pathway of melatonin, the last and key step is that N-acetylserotonin methyltransferase (ASMT) converts N-acetylserotonin into melatonin. Here, we identified an apple ASMT gene, MdASMT9, using homology-based cloning and in vitro enzyme assays. Overexpression of MdASMT9 significantly increased melatonin accumulation in transgenic apple lines. Moreover, an enhanced WUE was observed in the MdASMT9-overexpressing apple lines. Under well-watered conditions, this increase in WUE was attributed to an enhancement of photosynthetic rate and stomatal aperture via a reduction in abscisic acid biosynthesis. By contrast, under long-term moderate water deficit conditions, regulations in photoprotective mechanisms, stomatal behavior, osmotic adjustment and antioxidant activity enhanced the WUE in transgenic apple lines. Taken together, our findings shed light on the positive effect of MdASMT9 on improving WUE of apple by modulating melatonin biosynthesis.
面对全球气候变化，提高苹果水利用效率（WUE）变得越来越重要。褪黑素是一种多效分子，在植物发育和胁迫耐受中发挥作用。在苹果中，外源施用褪黑素已得到广泛研究，但褪黑素的生物合成及其生理作用仍不清楚。在植物褪黑素的生物合成途径中，最后也是关键的一步是 N-乙酰血清素甲基转移酶（ASMT）将 N-乙酰血清素转化为褪黑素。在这里，我们使用基于同源性的克隆和体外酶测定法鉴定了一个苹果 ASMT 基因 MdASMT9。MdASMT9 的过表达显著增加了转基因苹果系中褪黑素的积累。此外，在 MdASMT9 过表达的苹果系中观察到 WUE 的增强。在充分浇水的条件下，这种 WUE 的增加归因于通过减少脱落酸生物合成来增强光合速率和气孔开度。相比之下，在长期中度水分亏缺条件下，光保护机制、气孔行为、渗透调节和抗氧化活性的调节增强了转基因苹果系的 WUE。总之，我们的研究结果表明，MdASMT9 通过调节褪黑素的生物合成对提高苹果的 WUE 具有积极作用。
