4月9日，我校植物营养生物学团队在Plant Physiology上发表了题为“OsWRKY37 acts as a positive regulator for flowering time and grain fertility in rice under copper deficient condition”的研究论文，揭示了缺铜条件下转录因子OsWRKY37调控铜吸收运输影响水稻开花结实的分子机制。
铜是植物生长发育所必需的微量营养元素，也是对水稻花器官发育和产量形成影响最大的微量元素；缺铜易导致水稻开花期推迟、花药形成受阻、花粉活性下降、结实率降低、无效分蘖增加，从而严重影响水稻籽粒产量。近年来，我国高强度、集约化土地利用方式及作物复种比例的增加，加剧了土壤养分的携出量，降低了土壤肥力水平；同时，由于耕作过程中忽视微量元素肥料施用，引起土壤养分比例失衡，极易导致耕地铜缺乏，从而影响水稻正常的生殖生长及产量形成。随着科学研究的不断探索以及对水稻基因功能的逐步解析，参与水稻铜吸收和运输过程的重要基因特别是转运基因不断被克隆和鉴定，在水稻中逐渐形成了一个清晰的铜运输路径，然而该过程的上游调控因子及其具体的调控网络尚不清楚。
课题组前期对不同铜水平处理下的水稻根系进行转录组分析，获得一个受缺铜诱导表达功能未知的WRKY转录因子OsWRKY37。荧光定量PCR和ProOsWRKY37:GUS转基因植株分析结果显示，OsWRKY37主要在根、叶片、叶枕、节的维管组织、新生小穗以及花药中表达。缺铜条件下，超量表达OsWRKY37促进水稻根系对铜的吸收以及铜从根向地上部的转运；而敲除突变OsWRKY37抑制铜从根向地上部的转运以及向小穗的分配，显著降低雄蕊中的铜含量，影响花粉发育；敲除突变体表现为开花期推迟、育性降低、籽粒产量下降（图1）。酵母单杂交、烟草瞬时表达、EMSA和ChIP-qPCR等试验证明，OsWRKY37可与铜转运基因OsCOPT6及OsYSL16启动子中的W-box相互结合，并上调其表达水平（图2）。总而言之，缺铜诱导OsWRKY37表达，OsWRKY37可与OsCOPT6和OsYSL16的启动子相互结合，正向调控其表达水平，促进水稻根系对铜的吸收以及铜从根向地上部和小穗中转运，有利于花器官正常发育及籽粒产量形成。
图1 缺铜条件下敲除突变OsWRKY37影响开花期及籽粒产量
图2 OsWRKY37可与OsCOPT6和OsYSL16启动子相互结合
图3 OsWRKY37调控OsCOPT6和OsYSL16促进铜吸收运输的作用模式图
我校资源与环境学院已毕业博士研究生姬晨晨为第一作者，蔡红梅副教授为通讯作者，已毕业博士研究生丁静丽和已毕业硕士研究生李海星、郁露参与了该研究，徐芳森教授、石磊教授、姜存仓教授、王创教授、丁广大教授和汪社亮副教授对该研究的试验设计和数据分析提供了宝贵的建议。本研究得到国家重点研发计划项目资助。
【英文摘要】
Efficient uptake, translocation, and distribution of Cu to rice (Oryza Sativa) spikelets is crucial for flowering and yield production. However, the regulatory factors involved in this process remain unidentified. In this study, we isolated a WRKY transcription factor gene induced by Cu deficiency, OsWRKY37, and characterized its regulatory role in Cu uptake and transport in rice. OsWRKY37 was highly expressed in rice roots, nodes, leaf vascular bundles, and anthers. Overexpression of OsWRKY37 promoted the uptake and root-to-shoot translocation of Cu in rice under -Cu condition but not under +Cu condition. While mutation of OsWRKY37 significantly decreased Cu concentrations in the stamen, the root-to-shoot translocation and distribution ratio in brown rice affected pollen development, delayed flowering time, decreased fertility, and reduced grain yield under -Cu condition. Y1H, transient co-expression and EMSAs, together with in situ RT-PCR and RT-qPCR analysis, showed that OsWRKY37 could directly bind to the upstream promoter region of OsCOPT6 (copper transporter) and OsYSL16 (yellow stripe-like protein) and positively activate their expression levels. Analyses of oscopt6 mutants further validated its important role in Cu uptake in rice. Our study demonstrated that OsWRKY37 acts as a positive regulator involved in the uptake, root-to-shoot translocation, and distribution of Cu through activating the expression of OsCOPT6 and OsYSL16, which is important for pollen development, flowering, fertility, and grain yield in rice under Cu deficient conditions. Our results provide a genetic strategy for improving rice yield under Cu deficient condition.
