弱光下水稻光合效率的基因挖掘及其育种应用

Rice (Oryza Sativa L.) is the major crop in China. The enhancement of rice production is the central target for security of food staple in the long-term way. However, increasingly occurrence of stressed climates, such as frog, heavy cloudy weather, has detrimental effects on the rice production. Additionally, rice is a plant with multiple tiller, while 70% leaves exposed to low light regimes. Thus, improving photosynthetic efficiency under low light at canopy levels is the key way to address the increase in rice production. Recently, genome-wide association study provides a new clue to explore the functional genes. In this study, we will focus on improving photosynthetic efficiency under low light, utilizing 217 Minicore rice collection, to explore biological significances as well as underlying molecular mechanisms of key candidate genes. In addition, with incorporation with CRISPR-DNA editing in rice and T-DNA mutagenesis in Arabidopsis, results have revealed that sdgfty gene is the key gene controlling photosynthetic efficiency under low light. The sdgfty gene belongs to SETDOMAIN gene family, interacting with photosynthetic carbon metabolic enzyme Rubisco. It is predicted that SDGFTY can act transferring methyl to specific lysine residues on Rubisco by catalyzing donor S-AdoMet, indeed resulting in modification of activities, spatial structures and reprogramming of carbon metabolic flow. In this study, to further uncover the molecular mechanism of sdgfty gene controlling photosynthetic efficiency under low light, a ranges of molecular biology, enzymatic chemistry and bioinformation will be integrated.

水稻是我国主要的粮食作物。然而，近年来长期的雾霾和阴云多雨已严重影响了我国水稻产量。另外，水稻冠层下部叶片常处于低光环境。因此，改善叶片低光利用率可为我国水稻粮食增产提供新的思路。全基因组关联分析已被成功应用于水稻各种经济性状的功能基因挖掘研究。本研究着眼于提高水稻低光光合利用效率，利用217份来自全球水稻微核心群体，挖掘关键候选基因。申请者已利用CRISPR基因功能缺失和T-DNA拟南芥突变体材料，证明了sdgfty基因很可能是调控低光光合效率的关键基因。该基因属于一个SETDOMAIN基因家族，与光合碳代谢关键酶Rubisco具有相互作用。据推测，其编码的蛋白可将甲基通过供体S-甲硫蛋氨酸转移至靶标Rubisco的特异赖氨酸残基上，进而起到活性修饰、空间结构变化和碳代谢流重译等功能。本项目将整合大量分子生物学、酶化学和生物信息学方法，深入挖掘sdgfty基因调控低光效率的分子机理。

水稻是我国第一大粮食作物，约占粮食总产量的40%。提高水稻产量，对于保障国家粮食安全至关重要。然而，近年来，非正常的极端气候环境出现频率骤增。长期雾霾等弱光天气已严重影响了我国水稻的经济产量（第二届中国粮食与食品安全战略峰会，2014）。因此如何提高适应弱光环境下的水稻产量对于实现我国高产稳产目标和国家粮食战略需求具有重要意义。本项目以204份来源于全球97个国家的水稻微核心种质资源为材料，系统调查了14个光合效率自然变异，利用特征选择和相关性分析，发现了其中4个光合参数与生物产量密切相关的光合参数，包括低光光合效率、气孔开关速度、暗呼吸和水分利用效率（Qu et al., 2017）。随后，我们利用Illumina平台，对204份材料进行DNA测序，获得20倍深度测序信息，最终产生2.3M的SNPs。通过全基因组关联分析发现了影响低光光合效率基因SDG40（Qu et al., unpublished）、气孔开关的重要基因NHX1（Qu et al., 2020）和叶片暗呼吸速率基因LRK1（Qu et al., 2020）。本项目鉴定到了NHX1和LRK1基因优良等位变异单倍型信息，并以常规高产水稻明辉63和02428为轮回亲本，构建了片段代换系，并证明含有优良等位变异的NHX1和LRK1水稻品系，可分别大幅度提高水稻的干旱和高温抗性。随后，通过启动子差异序列分析，发现了在NHX1启动子上游1530bp处，含有一个高光效EmBP1转录因子结合位点“CACGTG”（Perveen et al., 2020，第二作者），而另一种SNP的变异导致结合能力大幅度下降。这解释了NHX1基因表达在不同水稻材料中呈现差异的原因。相关专利已经提交（201910247625.0；PCT/CN2019/087976；2020031001048200；202010587199.8）。本项目提供的光合调控基因优良等位变异可为高光效分子模块耦合提供新的方案，助力于构建智能冠层光合元件库，有利于培育出综合逆境下（高温、干旱和低光）水稻的高产稳产新品种提供新思路。