Laboratory of Molecular Plant Pathology, School of Life Sciences and Biotechnology, Korea University, Anam-dong, Sungbuk-ku, Seoul 136-713, Korea.
Plant J. 2012 Dec;72(5):843-55. doi: 10.1111/tpj.12003. Epub 2012 Oct 12.
Loss-of-function alleles of the mildew resistance locus O (MLO) gene provide broad-spectrum powdery mildew disease resistance. Here, we identified a pepper (Capsicum annuum) MLO gene (CaMLO2) that is transcriptionally induced by Xanthomonas campestris pv. vesicatoria (Xcv) infection. Topology and subcellular localization analyses reveal that CaMLO2 is a plasma membrane-anchored and amphiphilic Ca²⁺-dependent calmodulin-binding protein. CaMLO2 expression is up-regulated by Xcv and salicylic acid, as well as abiotic stresses. Silencing of CaMLO2 in pepper plants confers enhanced resistance against virulent Xcv, but not against avirulent Xcv. This resistance is accompanied by a compromised susceptibility cell-death response and reduced bacterial growth, as well as an accelerated reactive oxygen species burst. Virulent Xcv infection drastically induces expression of the salicylic acid-dependent defense marker gene CaPR1 in CaMLO2-silenced leaves. CaMLO2 over-expression in Arabidopsis enhances susceptibility to Pseudomonas syringae pv. tomato and Hyaloperonospora arabidopsidis. Leaves of plants over-expressing CaMLO2 exhibit a susceptibility cell-death response and high bacterial growth during virulent Pst DC3000 infection. These are accompanied by enhanced electrolyte leakage but compromised induction of some defense response genes and the reactive oxygen species. Together, our results suggest that CaMLO2 is involved in the susceptibility cell-death response and bacterial and oomycete proliferation in pepper and Arabidopsis.
MLO 基因的功能丧失等位基因提供广谱白粉病抗性。在这里，我们鉴定了一个辣椒（Capsicum annuum）MLO 基因（CaMLO2），它可被丁香假单胞菌 pv.vesicatoria（Xcv）感染转录诱导。拓扑和亚细胞定位分析表明，CaMLO2 是一种质膜锚定的、两亲性的 Ca²⁺依赖的钙调蛋白结合蛋白。CaMLO2 的表达受 Xcv 和水杨酸以及非生物胁迫的上调。沉默辣椒中的 CaMLO2 赋予对强毒 Xcv 的增强抗性，但对无毒 Xcv 没有抗性。这种抗性伴随着易感性细胞死亡反应的受损和细菌生长的减少，以及活性氧爆发的加速。强毒 Xcv 感染极大地诱导了 CaMLO2 沉默叶片中水杨酸依赖防御标记基因 CaPR1 的表达。拟南芥中 CaMLO2 的过表达增强了对丁香假单胞菌 pv.番茄和 Hyaloperonospora arabidopsidis 的敏感性。过表达 CaMLO2 的植物叶片在强毒 Pst DC3000 感染期间表现出易感性细胞死亡反应和高细菌生长。这伴随着电解质泄漏的增强，但一些防御反应基因和活性氧的诱导受损。总之，我们的结果表明，CaMLO2 参与了辣椒和拟南芥中易感细胞死亡反应以及细菌和卵菌的增殖。
