Alternative oxidase (AOX) is a mitochondrial terminal oxidase which is responsible for an alternative route of electron transport in the respiratory chain. This nuclear-encoded enzyme is involved in a major path of survival under adverse conditions by transfer of electrons from ubiquinol instead of the main cytochrome pathway. AOX protects against unexpected inhibition of the cytochrome c oxidase pathway and plays an important role in stress tolerance. Two AOX subfamilies (AOX1 and AOX2) exist in higher plants and are usually encoded by small gene families. In this study, genome-wide searches and cloning were completed to identify and characterize AOX genes in cucumber (Cucumis sativus L.). Our results revealed that cucumber possesses no AOX1 gene(s) and only a single AOX2 gene located on chromosome 4. Expression studies showed that AOX2 in wild-type cucumber is constitutively expressed at low levels and is upregulated by cold stress. AOX2 transcripts and protein were detected in leaves and flowers of wild-type plants, with higher levels in the three independently derived mosaic (MSC) mitochondrial mutants. Because cucumber possesses a single AOX gene and its expression increases under cold stress and in the MSC mutants, this plant is a unique and intriguing model to study AOX expression and regulation particularly in the context of mitochondria-to-nucleus retrograde signaling.

中文翻译：

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黄瓜具有单一末端替代氧化酶基因，该基因在冷应激和镶嵌 (MSC) 线粒体突变体中上调

替代氧化酶 (AOX) 是一种线粒体末端氧化酶，负责呼吸链中电子传递的替代途径。这种核编码酶通过从泛醇而不是主要细胞色素途径转移电子，参与不利条件下的主要生存途径。AOX 可防止细胞色素 c 氧化酶途径的意外抑制，并在胁迫耐受中发挥重要作用。高等植物中存在两个 AOX 亚家族（AOX1 和 AOX2），通常由小基因家族编码。在这项研究中，完成了全基因组搜索和克隆以鉴定和表征黄瓜 (Cucumis sativus L.) 中的 AOX 基因。我们的研究结果表明，黄瓜没有 AOX1 基因，只有一个位于 4 号染色体上的 AOX2 基因。表达研究表明，野生型黄瓜中的 AOX2 以低水平组成型表达，并在冷胁迫下上调。在野生型植物的叶和花中检测到 AOX2 转录物和蛋白质，在三个独立衍生的镶嵌 (MSC) 线粒体突变体中水平较高。由于黄瓜具有单个 AOX 基因，并且其在冷胁迫和 MSC 突变体中的表达增加，因此该植物是研究 AOX 表达和调控的独特而有趣的模型，特别是在线粒体到细胞核逆行信号的背景下。