Southern Regional Collaborative Innovation Center for Grain and Oil Crops in China, College of Resources and Environmental Sciences, Hunan Agricultural University, Changsha, 410128, China.
Hunan Provincial Key Laboratory of Farmland Pollution Control and Agricultural Resources Use, Hunan Provincial Key Laboratory of Nutrition in Common University, National Engineering Laboratory on Soil and Fertilizer Resources Efficient Utilization, Changsha, 410128, China.
Plant Mol Biol. 2019 Jul;100(4-5):561-569. doi: 10.1007/s11103-019-00878-y. Epub 2019 May 3.
Plant defensin AtPDF2.6 is not secreted to the apoplast and localized in cytoplasm. AtPDF2.6 is mainly expressed in root vascular bundles of xylem parenchyma cell, and significantly induced by Cd stress. AtPDF2.6 detoxicate cytoplasmic Cd via chelation, thus enhanced Cd tolerance in Arabidopsis. In order to detoxify the heavy metal cadmium (Cd), plants have evolved several mechanisms, among which chelation represents the major Cd-detoxification mechanism. In this study, we aimed to identify a new defensin protein involved in cytoplasmic Cd detoxification by using plant molecular genetics and physiological methods. The results of bioinformatic analysis showed that the Arabidopsis thaliana defensin gene AtPDF2.6 has a signal peptide that may mediate its secretion to the cell wall. Subcellular localization analysis revealed that AtPDF2.6 is localized to the cytoplasm and is not secreted to the apoplast, whereas histochemical analysis indicated that AtPDF2.6 is mainly expressed in the root xylem parenchyma cells and that its expression is significantly induced by Cd. An in vitro Cd-binding assay revealed that AtPDF2.6 has Cd-chelating activity. Heterologous overexpression of AtPDF2.6 increased Cd tolerance in Escherichia coli and yeast, and AtPDF2.6 overexpression significantly enhanced Cd tolerance in Arabidopsis, whereas functional disruption of AtPDF2.6 decreased Cd tolerance. These data suggest that AtPDF2.6 detoxifies cytoplasmic Cd via chelation and thereby enhances Cd tolerance in Arabidopsis. Our findings accordingly challenge the commonly accepted view of defensins as secreted proteins.
植物防御素 AtPDF2.6 不会分泌到质外体，而是定位于细胞质中。AtPDF2.6 主要在木质部薄壁细胞的维管束中表达，并被 Cd 胁迫显著诱导。AtPDF2.6 通过螯合作用使细胞质中的 Cd 解毒，从而增强拟南芥对 Cd 的耐受性。为了解毒重金属镉（Cd），植物已经进化出几种机制，其中螯合作用是主要的 Cd 解毒机制。在这项研究中，我们使用植物分子遗传学和生理方法，旨在鉴定一种参与细胞质 Cd 解毒的新防御素蛋白。生物信息学分析的结果表明，拟南芥防御素基因 AtPDF2.6 具有一个信号肽，可能介导其分泌到细胞壁。亚细胞定位分析表明，AtPDF2.6 定位于细胞质，不会分泌到质外体，而组织化学分析表明，AtPDF2.6 主要在根木质部薄壁细胞中表达，其表达受到 Cd 的显著诱导。体外 Cd 结合实验表明，AtPDF2.6 具有 Cd 螯合活性。AtPDF2.6 的异源过表达增加了大肠杆菌和酵母的 Cd 耐受性，并且 AtPDF2.6 的过表达显著增强了拟南芥的 Cd 耐受性，而 AtPDF2.6 的功能缺失则降低了 Cd 耐受性。这些数据表明，AtPDF2.6 通过螯合作用使细胞质中的 Cd 解毒，从而增强拟南芥对 Cd 的耐受性。因此，我们的发现挑战了防御素作为分泌蛋白的普遍观点。
