水稻根中硒代蛋氨酸向茎叶转运的分子机制研究

Selenium (Se) is an essential micronutrient in humans and other animals. It plays indispensable roles in human health. People mainly acquire Se from plant foods, especially cereal foods. Rice is a staple crop in China, but Se content in brown rice is lower. Under submerged condition of paddy soils, rice plants absorb predominately selenite. After selenite enters rice roots, it is readily converted to organic Se such as selenomethionine as a dominant form and retains in roots, less is translocated to shoots. Thus, low efficiency for the transport of selenomethionine from roots to shoots is the bottleneck to improve Se content in brown rice. The physiological and molecular mechanism involved in the transport of selenomethionine by plants remains unclear until now. Therefore, we will identify the amino acid transporter responsible for selenomethionine transport based on the known T-DNA insertion mutants. By means of RT-PCR, in situ hybrid, GFP fluorescence, HPLC-ICP-MS, and genetically modified techniques, specific transport process and transport efficiency of amino acid transporters for selenomethionine from roots to shoots will be investigated to elucidate the key process controlling selenomethionine transport. In this study, molecular mechanism of selenomethionine transport from roots to shoots will be uncovered, which provides important theoretical basis for breeding selenium-enriched varieties of rice.

硒是人和动物必需的微量元素，在人体健康中具有不可替代的作用。人们主要从植物性食物尤其谷物中摄取硒。水稻是我国主要的粮食作物，但稻米硒含量较低。在稻田淹水条件下，水稻主要吸收亚硒酸盐。亚硒酸盐进入水稻根后易于转化为硒代蛋氨酸为主要形式的有机硒而滞留在根中，向茎叶转运较少。因此水稻转运硒代蛋氨酸效率低是制约稻米硒含量提高的瓶颈。然而目前有关植物转运硒代蛋氨酸的生理和分子机制尚不清楚。本项研究利用筛选到的已知T-DNA插入位点的水稻氨基酸突变体，鉴定具有转运硒代蛋氨酸功能的氨基酸转运蛋白，并利用RT-PCR、原位杂交、GFP荧光、HPLC-ICP-MS以及转基因等手段，探讨氨基酸转运蛋白所涉及的具体转运过程，从而阐明控制根中硒代蛋氨酸向茎叶转运的关键步骤。本项研究将揭开水稻根中硒代蛋氨酸向茎叶转运的分子机制，从而为富硒水稻品种的选育提供重要的理论依据。

硒是人和动物必需的微量元素。世界上有近10亿人处于缺硒状态，尤其以谷物为主食的人群。水稻是世界一半以上人口的主食。在淹水条件下，亚硒酸盐是土壤中主要的有效硒形式。亚硒酸盐被水稻根系吸收后，主要转化为硒代蛋氨酸等形式有机硒而滞留根内，因此成为提高稻米硒含量的瓶颈。然而，直到目前，人们对植物转运硒代蛋氨酸的机制并不清楚。我们过去证明了PTR家族的硝酸盐转运蛋白NRT1.1B在硝酸盐吸收和转运过程中扮演着重要作用。有趣的是，用硒代蛋氨酸处理，与过表达空载体的酵母相比，过表达NRT1.1B cDNA株系累积较高的硒；注射NRT1.1B cRNA 的蛙卵细胞也比注射水累积较多的硒。这些结果表明NRT1.1B呈现体外转运硒代蛋氨酸活性。在突变体nrt1.1b中，硒代蛋氨酸转运明显降低。过表达NTR1.1B 可以显著提高总硒和硒代蛋氨酸含量以及籽粒硒含量，尤其是维管特异性表达植株籽粒硒含量提高到1.8倍。我们的研究结果有力地证明了NRT1.1B具有转运硒代蛋氨酸的功能，表明它是通过促进硒转运而提高籽粒硒含量的有潜力的候选转运蛋白。目前研究将会加深人们对硒代谢产物硒代蛋氨酸向茎叶转运的理解，并为选育富硒水稻品种提供新的思路。