Department of Biology and Biotechnology 'Charles Darwin', Sapienza University of Rome, Piazzale Aldo Moro 5, 00185, Rome, Italy.
Department MESVA, University of L'Aquila, L'Aquila, Italy.
Plant J. 2018 Apr;94(2):260-273. doi: 10.1111/tpj.13852. Epub 2018 Mar 15.
Recognition of endogenous molecules acting as 'damage-associated molecular patterns' (DAMPs) is a key feature of immunity in both animals and plants. Oligogalacturonides (OGs), i.e. fragments derived from the hydrolysis of homogalacturonan, a major component of pectin are a well known class of DAMPs that activate immunity and protect plants against several microbes. However, hyper-accumulation of OGs severely affects growth, eventually leading to cell death and clearly pointing to OGs as players in the growth-defence trade-off. Here we report a mechanism that may control the homeostasis of OGs avoiding their deleterious hyper-accumulation. By combining affinity chromatography on acrylamide-trapped OGs and other procedures, an Arabidopsis thaliana enzyme that specifically oxidizes OGs was purified and identified. The enzyme was named OG OXIDASE 1 (OGOX1) and shown to be encoded by the gene At4g20830. As a typical flavo-protein, OGOX1 is a sulphite-sensitive H O -producing enzyme that displays maximal activity on OGs with a degree of polymerization >4. OGOX1 belongs to a large gene family of mainly apoplastic putative FAD-binding proteins [Berberine Bridge Enzyme-like (BBE-like); 27 members], whose biochemical and biological function is largely unexplored. We have found that at least four BBE-like enzymes in Arabidopsis are OG oxidases (OGOX1-4). Oxidized OGs display a reduced capability of activating the immune responses and are less hydrolysable by fungal polygalacturonases. Plants overexpressing OGOX1 are more resistant to Botrytis cinerea, pointing to a crucial role of OGOX enzymes in plant immunity.
内源性分子识别作为“损伤相关分子模式”（DAMPs）是动物和植物免疫的一个关键特征。寡半乳糖醛酸（OGs），即源自果胶主要成分同质半乳糖醛酸水解的片段，是激活免疫并保护植物免受几种微生物侵害的一类众所周知的 DAMPs。然而，OGs 的过度积累严重影响生长，最终导致细胞死亡，并清楚地表明 OGs 是生长与防御权衡中的参与者。在这里，我们报告了一种可能控制 OGs 内稳态的机制，避免其有害的过度积累。通过在丙烯酰胺捕获的 OGs 上进行亲和层析和其他程序的组合，我们纯化并鉴定了一种特异性氧化 OGs 的拟南芥酶。该酶被命名为 OG 氧化酶 1（OGOX1），并被证明由 At4g20830 基因编码。作为一种典型的黄素蛋白，OGOX1 是一种亚硫酸盐敏感的 H2O 产生酶，对聚合度>4 的 OGs 显示最大活性。OGOX1 属于一个大型基因家族，主要是质外体假定的 FAD 结合蛋白[小檗碱桥接酶样（BBE-like）; 27 个成员]，其生化和生物学功能在很大程度上尚未探索。我们发现拟南芥中至少有四个 BBE-like 酶是 OG 氧化酶（OGOX1-4）。氧化的 OGs 显示出降低激活免疫反应的能力，并且更难被真菌多聚半乳糖醛酸酶水解。过表达 OGOX1 的植物对 Botrytis cinerea 的抗性更强，这表明 OGOX 酶在植物免疫中起着至关重要的作用。
