水稻低温白叶突变体wll1的基因克隆及功能研究

Rice is one of the most important food crops in our country. High-yield breeding is the most effective safeguard for food safty and agricultural sustainable development. The photosynthesis is one of the predominant influences for rice yield determination,and the photosynthetic efficiency is decided largely by leaf color. Albino (white leaf) mutant is an usual type of leaf color mutants in high plants. We found a albino mutant, named wll1 (white leaf under low temperature)from cultivar 93-11. This mutant shows white leaf under low temperature during seedling stage, but turns to green in four-leaf stage. The result of primary mapping suggest WLL1 is an new gene related to leaf color. Here we plan to fine mapping and clone this gene, analyse the physiological indexes including chlorophyll content, photosynthetic rate and chloroplast ultrastructure of wild type and wll1 mutant while turning to green before or after, and study the gene expression pattern and the physiological fuction of the coden protein to find the molecular mechanism how WLL1 regulate the rice leaf color, chlorophyll synthesis or chloroplast development. Meanwhile we will detect the expression of other genes related to leaf color to elaborate further the molecular mechanism of chlorophyll sybthesis and chloroplast development. All these results would provide the firm foundation for the application of leaf color marker, the improvement for hybrid rice seeds' purity, and rice high photosynthetic efficiency breeding.

水稻是我国最重要的粮食作物之一。高产育种是确保我国粮食安全和农业可持续发展最有效的保障。光合作用是水稻产量形成的关键因素之一，而叶色在很大程度上决定了光合作用的效率。白叶突变体是高等植物叶色突变中较常见的一种突变类型。现在我们发现一个诱变自93-11的新白叶突变体wll1，在低温环境下苗期叶片为白色、4叶期后完全转绿。初步定位表明这是一个新的叶色相关基因。本研究计划精细定位并图位克隆该突变体基因，分析野生型和wll1突变体转绿前后在叶绿素含量、光合速率等生理指标及叶绿体超微结构的差异，研究基因表达模式和蛋白生理功能，阐明WLL1基因调控水稻叶色、叶绿素合成或叶绿体发育的分子机理。同时检测其它叶色相关基因的表达，进一步阐明叶绿素生物合成和叶绿体发育的分子机理，为叶色标记应用、杂交稻生产的田间纯度提高及水稻高光效育种等提供坚实的理论依据。

本项目以一个93-11EMS诱变的低温苗期白条纹叶突变体wll1为材料， wll1在低温(23℃)下白条纹，高温(28℃)与野生型没有差异；其叶绿素含量显著、净光合速率显著下降，叶绿体结构异常。利用图位克隆的方法分离了WLL1基因，其编码蛋白为假尿嘧啶合酶，转基因功能互补实验证实了该基因功能。WLL1在水稻植株中组成型表达，但是在叶片等绿色组织中表达最高，其编码蛋白亚细胞定位与叶绿体。对突变体中叶绿素合成、叶绿体发育及光合作用相关基因的表达分析表明相关基因多数在突变体中下调表达。本项目结果表明WLL1在水稻叶绿素合成、叶绿体发育及光合作用中起着非常重要的作用。为全面阐明水稻叶绿素生物合成与叶绿体发育的分子机理、叶色标记应用于杂交稻纯度鉴定、提高杂交稻生产的田间纯度及水稻高光效育种等提供坚实的理论依据。