水稻OsNRAMP2基因调控谷粒镉积累的功能和机制研究

In the past few years, cadmium contamination of rice grain has been a hot topic in China and brings great threats to the safety of food production and people’s health. It is critical to understand the molecular and physiological mechanisms of low cadmium accumulation for safety rice production. In the previous study, we have identified a major QTL associated with cadmium accumulation in grain, designated as qCd3-2. The candidate gene, OsNRAMP2 was determined based on gene annotation, differential gene expression analysis, gene sequence analysis and yeast experiments. In this proposed project, gene knockout and overexpression will be used to confirm the function of OsNRAMP2 in grain cadmium accumulation in rice; the regulatory mechanism of OsNRAMP2 in grain cadmium accumulation in rice will be investigated through integrated analysis of the cadmium contents and expression levels in various tissues at different growth stage. In addition, the effects of different alleles and their expression levels of OsNRAMP2 on grain cadmium accumulation and some important agronomic traits will be analyzed to evaluate its potential use in rice production. With the successful completion of this project, it will provide new insights in the molecular and physiological mechanisms of grain cadmium accumulation in rice, and laydown basis for molecular breeding for low grain cadmium accumulation in rice.

近年来水稻镉污染问题已成为社会的热点，对我国粮食安全生产和人民健康构成了巨大的威胁。探明水稻低镉积累分子生理，对保障水稻安全生产意义重大。前期我们通过全基因组关联分析鉴定到一个与谷粒镉积累有关的主效QTL（qCd3-2），进一步通过基因注释、基因差异表达分析、基因结构分析和酵母试验确定其候选基因为OsNRAMP2。本项目将在前期研究基础上，通过基因敲除、增量表达等转基因技术确认OsNRAMP2在水稻谷粒镉积累中的功能；通过不同生育期和器官组织中的镉含量，以及OsNRAMP2的表达特征分析OsNRAMP2在水稻谷粒镉积累过程的调控机理；通过分析OsNRAMP2基因型和表达对水稻谷粒镉积累和重要农艺性状的影响，以了解OsNRAMP2在水稻育种中的应用前景。项目的成功实施可为水稻谷粒镉积累分子机理的阐明提供新的知识，并为低镉水稻的分子育种奠定基础。

稻米中镉(Cd)的积累会引起一系列的健康问题。鉴定与谷粒Cd积累有关的基因并进行分子育种是减少Cd积累的有效途径。在这项研究中，敲除水稻OsNRAMP家族成员OsNRAMP2，使谷粒Cd浓度降低了38%以上，过表达OsNRAMP2使谷粒Cd浓度增加了50%以上。生理实验表明，OsNRAMP2通过正向调节Cd从液泡流出，促进Cd从根到茎的转运。在灌浆期，OsNRAMP2在除壳外的所有组织中均高表达，提示其在Cd再动员中的作用。OsNRAMP2表达的变化影响了籽粒中Fe、Mn、Zn和Cu的浓度，也影响了水稻的生长。系统发育分析表明，OsNRAMP2单倍型在粳稻和籼稻中的分布存在差异。在OsNRAMP2的4个单倍型中，外显子1插入6 bp核苷酸的Hap 1的谷粒Cd浓度至少比其他3个单倍型低45.3%。在水稻基因组3K序列中，几乎所有粳稻(99.3%)均携带OsNRAMP2的Hap 1，而籼稻(4.44%)很少携带Hap 1。本研究揭示了谷粒Cd积累的分子机制，为低Cd水稻的分子育种提供了一个有前景的靶点。