Synthesis of melatonin in mitochondria was reported in animals. However, there is no report on whether plant mitochondria also produce melatonin. Herein, we show that plant mitochondria are a major site for melatonin synthesis. In an in vitro study, isolated apple mitochondria had the capacity to generate melatonin. Subcellular localization analysis documented that an apple SNAT isoform, MzSNAT5, was localized in the mitochondria of both Arabidopsis protoplasts and apple callus cells. The kinetic analysis revealed that the recombinant MzSNAT5 protein exhibited high enzymatic activity to catalyze serotonin to N‐acetylserotonin with the K_m and V_max of 55 μmol/L and 0.909 pmol/min/mg protein at 35°C, respectively; this pathway functioned over a wide range of temperatures from 5 to 75°C. In an in vivo study, MzSNAT5 was drought inducible. The transgenic Arabidopsis ectopically expressing MzSNAT5 elevated the melatonin level and, hence, enhanced drought tolerance. The mechanistic study indicated that the ectopically expressing MzSNAT5 allows plant mitochondria to increase melatonin synthesis. As a potent free radical scavenger, melatonin reduces the oxidative stress caused by the elevated reactive oxygen species which are generated under drought stress in plants. Our findings provide evidence that engineered melatonin‐enriched plants exhibit enhanced oxidative tolerance.

中文翻译：

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植物线粒体合成褪黑激素并增强植物对干旱胁迫的耐受性

据报道，动物体内线粒体中褪黑激素的合成。但是，没有关于植物线粒体是否也产生褪黑激素的报道。在这里，我们表明植物线粒体是褪黑激素合成的主要场所。在体外研究中，分离出的苹果线粒体具有产生褪黑激素的能力。亚细胞定位分析表明，苹果SNAT亚型MzSNAT5位于拟南芥原生质体和苹果愈伤组织细胞的线粒体中。动力学分析表明，重组MzSNAT5蛋白具有很高的酶促活性，可将5-羟色胺转化为N-乙酰5-羟色胺，_最大K _m和V _max。在35°C下分别为55μmol/ L和0.909 pmol / min / mg蛋白; 该途径可在5至75°C的宽温度范围内发挥作用。在体内研究中，MzSNAT5是干旱诱导的。异位表达MzSNAT5的转基因拟南芥提高了褪黑激素水平，因此增强了耐旱性。机理研究表明，异位表达的MzSNAT 5可使植物线粒体增加褪黑激素的合成。作为一种有效的自由基清除剂，褪黑激素可减少因干旱胁迫而在植物中产生的升高的活性氧所引起的氧化应激。我们的发现提供了证据，表明工程化的富含褪黑激素的植物表现出增强的氧化耐受性。