水稻根茎阻滞镉向籽粒富集的遗传基础研究

Soil cadmium (Cd) contamination has become a potential agricultural and environmental hazard worldwide and posed a serious problem for safe food production. Rice, an important staple food for nearly a half of the world's population, is a major source of Cd intake. A number of approaches have been proposed to reduce the accumulation of Cd in rice grains. One of the simplest and most cost-effective approaches would be to breed commercial rice with low Cd accumulation. A better understanding of the molecular mechanism of Cd retention in rice root and stem will facilitate the breeding program which requires introduce the Cd retention gene into agronomically improved rice varieties. In our previous study, we investigated genotypic variation in seed Cd concentration in more than 400 accessions from a rice core collection. The indica accession 9311 and the japonica accession nipponbare were identified as high and low Cd-accumulating accessions. The research proposed herein aims to address the molecular mechanism responsible for the difference of Cd retention between 9311 and nipponbare in root and stem. The aims of this study are: (1) to physiologically characterize and quantify the Cd retention in root and stem in 9311 and nipponbare; (2) to identify quantitative trait loci (QTLs) controlling seed Cd concentration and to fine map the major QTL; and (3) to develop molecular marker closely linked to QTLs for genetic improvement of commercial rice with high Cd accumulation. The success of this project will improve our knowledge on the molecular mechanism underlying the Cd retention in rice, and benefit breeding program to lower grain Cd accumulation.

日益严重的稻田镉污染给我国稻米品质带来严重威胁，培育符合安全标准的低镉高产水稻品种需要对现有的低镉资源品种或高产推广品种进行定向改造。开展低镉水稻根茎阻滞镉向籽粒富集的遗传基础研究，有利于揭示水稻根茎对镉的屏障作用分子机理，为低镉高产水稻育种提供分子手段。本项目将首先比较低镉稻米水稻品种（nipponbare）和高镉稻米水稻品种（9311）根茎对镉截留能力的差异。然后利用已经构建的9311与nipponbare重组自交系群体对水稻根茎阻滞镉向籽粒富集的遗传基础进行研究，定位与低镉相关的QTL并对主效QTL进行精细定位。在此基础上，开发出与低镉相关的分子标记并通过分子育种手段将控制低镉稻米的基因组片段导入到9311基因组中，培育出低镉水稻新材料。预期研究成果可以丰富人们对稻米镉富集的遗传基础的理解，为最终克隆控制镉向稻米中转运的基因打下基础，同时还可以为低镉水稻分子育种提供分子标记。

日益严重的稻田镉（Cadmium，Cd）污染给我国稻米品质带来严重威胁。开展水稻根茎阻滞Cd向籽粒富集的遗传基础研究，有利于揭示水稻稻米Cd积累的分子机理，同时可以获得与低Cd稻米基因连锁的分子标记，为低Cd高产水稻育种提供分子手段。本项目利用Cd低积累稻品种日本晴（nipponbare）和Cd高积累籼稻品种93-11间的两个遗传群体，包括重叠导入系（Chromosome Segment Substitution Lines，CSSLs）和F2:3家系，对控制水稻根茎阻滞Cd向籽粒富集的主效QTLs进行遗传定位；根据表型变异，我们在第七染色体ID414和ID1279之间检测到一个能影响籽粒内Cd积累的主效QTL——qCd7，并根据遗传比较作图和酵母试验确定OsHMA3为qCd7的候选基因；该基因的自然变异分析表明，而来自nipponbare的基因型HMA3-1能够显著降低93-11背景下近等基因系的稻米Cd积累而对产量相关性状没有影响；而来自93-11的基因型HMA3-2属于弱等位基因；根据候选基因关联分析发现SNP7、SNP11与表型变异显著相关，并开发了功能标记Caps7；进化分析显示该基因存在较为明显的籼-粳分化现象；本项目的理论研究结果将有利于加深水稻籽粒Cd积累形成的分子遗传机制的理解，低积累的93-11近等基因系是优异的育种材料，开发的低镉分子标记可以为低镉育种提供筛选工具。

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