Duan Shuo, Jia Hongge, Pang Zhiqian, Teper Doron, White Frank, Jones Jeffrey, Zhou Changyong, Wang Nian
Citrus Research Institute, Southwest University, Chongqing, 400712, China.
Department of Microbiology and Cell Science, Citrus Research and Education Center, Institute of Food and Agricultural Sciences (IFAS), University of Florida, Lake Alfred, FL 33850, USA.
Mol Plant Pathol. 2018 Feb 20;19(8):1908-16. doi: 10.1111/mpp.12667.
Xanthomonas citri ssp. citri (Xcc) is an important plant-pathogenic bacterium that causes citrus canker disease worldwide. PthA, a transcriptional activator-like (TAL) effector, directs the expression of the canker susceptibility gene CsLOB1. Here, we report our recent progress in the functional characterization of CsLOB1. Subcellular localization analysis of CsLOB1 protein in citrus protoplast revealed that CsLOB1 is primarily localized in the nucleus. We showed that CsLOB1 expression driven by dexamethasone (DEX) in CsLOB1-GR transgenic plants is associated with pustule formation following treatment with DEX. Pustule formation was not observed in DEX-treated wild-type plants and in non-treated CsLOB1-GR transgenic plants. Water soaking is typically associated with symptoms of citrus canker. Weaker water soaking was observed with pustule formation in CsLOB1-GR transgenic plants following DEX treatment. When CsLOB1-GR-transgenic Duncan grapefruit leaves were inoculated with Xcc306ΔpthA4 and treated with DEX, typical canker symptoms, including hypertrophy, hyperplasia and water soaking symptoms, were observed on DEX-treated transgenic plant leaves, but not on mock-treated plants. Twelve citrus genes that are induced by PthA4 are also stimulated by the DEX-induced expression of CsLOB1. As CsLOB1 acts as a transcriptional factor, we identified putative targets of CsLOB1 via bioinformatic and electrophoretic mobility shift assays. Cs2g20600, which encodes a zinc finger C3HC4-type RING finger protein, has been identified to be a direct target of CsLOB1. This study advances our understanding of the function of CsLOB1 and the molecular mechanism of how Xcc causes canker symptoms via CsLOB1.
柑桔溃疡病菌（Xanthomonas citri ssp. citri，Xcc）是一种重要的植物病原细菌，在全球范围内引发柑桔溃疡病。转录激活样效应因子（TAL）PthA可调控溃疡病感病基因CsLOB1的表达。在此，我们报告了CsLOB1功能特性研究的最新进展。对柑桔原生质体中CsLOB1蛋白的亚细胞定位分析表明，CsLOB1主要定位于细胞核。我们发现，在CsLOB1-GR转基因植物中，地塞米松（DEX）驱动的CsLOB1表达与DEX处理后脓疱的形成有关。在DEX处理的野生型植物和未处理的CsLOB1-GR转基因植物中未观察到脓疱形成。水浸通常与柑桔溃疡病症状相关。DEX处理后，CsLOB1-GR转基因植物中脓疱形成时观察到较弱的水浸现象。用Xcc306ΔpthA4接种CsLOB1-GR转基因邓肯葡萄柚叶片并进行DEX处理后，DEX处理的转基因植物叶片上出现了典型的溃疡病症状，包括肥大、增生和水浸症状，而模拟处理的植物上未出现。PthA4诱导的12个柑桔基因也受到DEX诱导的CsLOB1表达的刺激。由于CsLOB1作为转录因子发挥作用，我们通过生物信息学和电泳迁移率变动分析确定了CsLOB1的假定靶标。已确定编码锌指C3HC4型泛素连接酶蛋白的Cs2g20600是CsLOB1的直接靶标。本研究增进了我们对CsLOB1功能以及Xcc如何通过CsLOB1导致溃疡病症状的分子机制的理解。
