Department of Medical Laboratory Science and Biotechnology, Central Taiwan University of Science and Technology, Taichung 406, Taiwan.
J Agric Food Chem. 2011 Sep 14;59(17):9290-302. doi: 10.1021/jf2024006. Epub 2011 Aug 5.
The gram-negative plant pathogenic Xanthomonas campestris pv. campestris (Xcc) is the causative agent of black rot in crucifers, a disease causing tremendous loss in agriculture. Copper-containing bactericides have been widely used to control this disease for many years, possibly leading to the development of copper resistance in Xcc. Homologues of copper resistance genes copLAB are present in the Xcc genome, but none has been characterized. In this study, mutations in copL, copA, and copB decreased Xcc copper tolerance. Among them, the copA mutant displayed the most significant reduction. The copA mutant also resulted in a reduction in virulence on the host cabbage. Sequence and mutational analysis demonstrated that copA encodes a multicopper oxidase and that CopA is able to catalyze the oxidation of 2,6-dimethoxyphenol. Alanine substitutions in each of the putative copper binding residues (H538, H583, C584, and H585) of CopA caused a loss of function including copper tolerance and oxidase activity. Furthermore, reporter assays showed that copA transcription is inducible in the presence of copper, subject to catabolite repression, and repressed under conditions of high osmolarity, nitrogen starvation, or oxygen limitation. This is the first time that multicopper oxidase has been characterized in the crucifer pathogen Xcc.
革兰氏阴性植物病原菌野油菜黄单胞菌（Xcc）是十字花科黑腐病的病原体，这种疾病会给农业造成巨大损失。多年来，含铜杀菌剂被广泛用于防治这种疾病，这可能导致 Xcc 产生铜抗性。Xcc 基因组中存在铜抗性基因 copLAB 的同源物，但尚未对其进行特征描述。在本研究中，copL、copA 和 copB 的突变降低了 Xcc 的铜耐受性。其中，copA 突变体的铜耐受性降低最为显著。copA 突变体还导致对宿主白菜的毒力降低。序列和突变分析表明，copA 编码一种多铜氧化酶，CopA 能够催化 2,6-二甲氧基苯酚的氧化。CopA 中每个假定铜结合残基（H538、H583、C584 和 H585）的丙氨酸取代导致功能丧失，包括铜耐受性和氧化酶活性丧失。此外，报告基因实验表明，copA 的转录在铜存在的情况下可被诱导，受分解代谢物阻遏，在高渗透压、氮饥饿或缺氧条件下受到抑制。这是首次在十字花科病原菌 Xcc 中对多铜氧化酶进行特征描述。
