转录因子OsbZIPX2提高水稻孕穗期耐低温分子机理研究

Low temperature is one of the major constraints in rice production. It is significant important that cloning tolerance to low temperature genes and cultivating new rice varieties resistant to abiotic stresses. We using a genome-wide association study (GWAS) in a population 203 cultivated rice varieties treated with low temperature during rice booting stage, and analysised each side of the peak SNPs, and identified a new loci associated gene with low temperature, OsbZIPX2. We found that OsbZIPX2 was quickly induced by low temperature during both booting stage and flowering stage. Transgenic plants analysis showed that OsbZIPX2 overexpressing had not improved rice tolerance to low temperature, but OsbZIPX2 RNAi transgenic plant showed sensitive to low temperature. Furthermore, we found that OsbZIPX2 can form heterodimer with OsbZIPX1 in yeast. Moreover, OsbZIPX1 overexpressing and OsbZIPX2 overexpressing hybrid lines have greatly increased rice tolerance to low temperature during reproductive stage. In this study, we would like to investigate conforming that OsbZIPX1 interact with OsbZIPX2; exploring OsbZIPX2 directly target genes and influence factors; the mechanism of OsbZIPX1 and OsbZIPX2 involved in abiotic stress response by using genetics, cellular biology, molecular biology, and biochemistry means, and also explore their possible application in rice low temperature tolerance improvement.

孕穗期低温是水稻生产的主要限制性因子之一，克隆重要应用价值的孕穗期耐低温基因并培育耐逆水稻新品种具有重要意义。前期对203个栽培稻进行孕穗期低温筛选，利用全基因组关联分析（GWAS）获得一个低温相关基因OsbZIPX2。OsbZIPX2在孕穗期和开花授粉期受低温诱导，过表达OsbZIPX2不能提高水稻对低温的耐受性，RNAi却对低温敏感。酵母双杂表明OsbZIPX2与OsbZIPX1互作。过表达OsbZIPX2与过表达OsbZIPX1杂交株系显著提高了水稻对低温的耐受性。本申请拟结合遗传学、细胞生物学、分子生物学和生化等技术手段进一步明确OsbZIPX1和OsbZIPX2的互作；OsbZIPX2调控的下游靶基因；OsbZIPX1协同调控OsbZIPX2响应低温逆境胁迫的分子机制及其影响因素，包括对靶基因的结合及转录活性的影响；探讨OsbZIPX1和OsbZIPX2在水稻耐低温改良的有效途。

低温严重影响水稻的地理分布、生长发育及产量。近年来，极端气候频繁增多，倒春寒、寒露风等低温灾害逐年增加。每年我国因低温造成的粮食损失高达3-5亿吨，严重影响着粮食供给。亚洲栽培稻（俗称水稻）分为籼稻和粳稻两个亚种。一般而言，籼稻主要种植在热带和亚热带地区，而粳稻由于比籼稻具有更强的低温耐受性多种植在温带地区。随着水稻种植区的不断北移，揭示粳稻驯化过程中适应低温环境的分子机制，对于培育高纬度高海拔地区的低温耐受性水稻品种具有重要的理论和现实意义。本课题本课题基于关联分析和选择分析，对微核心种质资源群体的bZIP转录因子家族开展与耐低温的关联分析，结合群体遗传学进行选择分析，找到了bZIP基因家族中最关键的耐低温的基因bZIP73。进一步分析发现bZIP73基因编码区第511位置单核苷酸多态性（SNP）（+511 bp, G>A; +171 aa, Glu>Lys）决定了其籼粳分化及低温的耐受性差异。转基因及近等基因系（NIL）的实验表明，粳稻型的bZIP73(bZIP73Jap)更耐低温，且双基因bZIP71-bZIP73Jap极大提高水稻对低温的耐受力。生理实验表明，低温下，在bZIP71的协助下，bZIP73Jap通过抑制ABA合成基因来抑制ABA含量升高；同时激活过氧化物酶基因的表达，清除活性氧ROS，进而使水稻提高了对低温的耐受力。进化选择分析表明，bZIP73在野生稻的祖先中就受到了选择且在粳稻的进化中受到了选择。bZIP73Jap为改良南方籼稻品种对低温的耐受性以及水稻的向北扩张具有重要的意义。