水稻镉吸收和积累相关基因的发掘和功能鉴定

Rice (Oryza sativa L.) is one of the most important food crops worldwide. Nowadays, with the development of industry, the pollution of environment is increasingly serious, and in particular, the excess of cadmium in lots of farmland has become a great threat to food security. It is an urgent task to develop efficient strategies to minimise the transfer of toxic elements into human body by food chain. In recent years, our research team had collected 533 accessions of cultivated rice at the global scale which represent both the genetic diversity in cultivated species and the usefulness in rice improvement, and also had detected their cadmium concentrations in shoots and brown rice. We found these collections had great natural variations in cadmium concentrations in both shoots and brown rice, suggesting there was a possibility to identify new genes related to cadmium accumulation and consequently helps cultivate green rice with low cadmium content by using natural rice population. In our previous work, we had finished the planting, sampling and cadmium determination of these 533 collections in three different experimental fields which located at Wuhan in Hubei province, Lingshui in Hainan province and Youxian in Hunan province, respectively. Based on the cadmium concentrations of 533 collections and their sequence data, we had performed GWAS and obtained a few candidate loci with good reproducibility. In this project, we have selected rice accessions with significant difference in cadmium accumulation as parents of QTL mapping by screening the 533 collections, and then combine map-based cloning and GWAS to identify genes related to cadmium uptake and accumulation, and consequently help clarify the molecular basis of natural variation of rice cadmium concentrations and breed rice cultivars with low cadmium.

水稻是全世界最重要的粮食作物之一。然而，随着工业的发展，环境污染日益突出，我国不少耕地镉的超标成为了粮食安全的巨大威胁，亟需有效的方法阻控镉通过食物链进入人体。在我们收集的533份水稻种质材料中，不同品种的镉浓度存在极大的差异，说明通过自然资源发掘镉积累相关功能基因，进而培育低镉水稻具有可行性。我们前期已经完成了种质材料在湖北武汉、海南陵水和湖南攸县三处不同试验田间的种植、样品采集及镉浓度测定，并结合全基因组测序完成了GWAS分析，鉴定到多个效应显著且重复性好的功能区段。本项目拟在此基础上进一步从种质材料中筛选出镉吸收或转移存在显著差异的亲本组合，结合基于分子标记的遗传定位以及GWAS结果进行镉积累相关基因的发掘，并揭示水稻镉积累自然变异的遗传基础，为培育低镉水稻品种提供理论指导和技术支持。

水稻中过量的镉（Cd）积累会对人体健康构成潜在威胁。前人研究表明，水稻不同品种籽粒Cd浓度的差异，很大程度取决于Cd由根向茎转移的能力差异。然而，目前水稻自然群体中不同品种Cd转移率的差异情况还没有系统的研究。在前期工作中，我们收集了来自中国不同地方的水稻核心种质材料529份，并对这529份水稻核心种质进行了全基因组测序以及离子组的测试工作。基于此，我们分析了这529个不同水稻品种的Cd积累变异、以及镉由根向茎转移率的变异情况。我们发现，仅有11个品种具有极高的Cd从根到茎的转移率,且其中7个由OsHMA3两个已知的等位基因引起（即氨基酸第80位或380位变异）。结合QTL定位和酵母分析，我们鉴定到一个新的OsHMA3等位基因，且发现其与上述剩余4个品种中三个的高镉积累相关。不同水稻品种间的表达量分析显示，这三个含有OsHMA3新等位基因品种的表达量显著低于日本晴及其它品种。酵母异源表达显示，该等位基因编码蛋白的Cd运输活性显著低于正常功能的OsHMA3单倍型（即日本晴型）。进一步分析显示OsHMA3新单倍型的Cd转运活性减弱是由512位的甘氨酸取代精氨酸引起的。因此，我们认为这三个品种Cd从根到茎的高转移率是由于OsHMA3的表达量和蛋白活性同时降低引起的。综合来说，该水稻自然群体中Cd从根到茎转移率最高的11个品种中，至少10个可通过前述三种不同的OsHMA3等位变异来解释。基于这一研究，我们进一步阐述了水稻自然群体中部分品种Cd高积累的遗传机制。