Maintaining rice reproduction under high temperature stress:- identifying mechanisms and germplasm to increase crop resilience.

水稻是中国的主要作物，占世界水稻产量的36.9%。据估计，到2050年，粮食产量需要增加50%才能确保粮食安全。用于种植水稻的区域和种植时间由气候条件决定。中国各地都种植水稻；然而，种植的频率和可以实现高产的地区受到温度的限制。全球气候变暖对水稻平均产量产生负面影响，但也对产量差异产生负面影响，导致低产量的频率增加。此外，平均温度的升高对营养生长期和生殖生长期的长度有负向影响。花卉发育是植物育种和种子生产的关键，直接影响植物的产量。花粉形成对温度胁迫高度敏感；因此，开花期间的高温胁迫对当前和长期作物产量构成严重威胁。这是特别的情况，因为开花和结籽通常发生在一个单一的，短暂的植物发育阶段，这与营养相关的胁迫不同，如果条件随后改善，则无法挽救。高温会减少开花枝的数量，从而减少每株花的数量，然而花粉形成的异常会导致雄性不育，从而导致种子结实率下降。因此，如果不发展对生殖温度压力的适应能力，特别是考虑到全球气温上升和气候条件的不断变化，就有可能造成毁灭性的产量损失。然而，在物种和基因型之间，对高温的耐受性存在相当大的遗传变异。了解植物在生殖发育过程中如何应对热胁迫，有助于识别可操纵和利用的遗传性状，以提高作物的耐温性。该项目将通过开发对温度胁迫具有增强抗逆性的种质来解决这些问题。该计划还将详细了解在高温胁迫下繁殖过程中发生的分子和细胞学变化，以及赋予高温恢复力的机制。发展这种抗灾能力不仅可以扩大水稻种植面积，还可以扩大水稻种植的时间和频率。这将导致更高的水稻产量，但也将使产量更有弹性，而不受环境波动和全球气候变化的影响。环境控制的男性生育能力在开发杂交育种材料方面也有重要应用。因此，从该项目获得的知识和种质将直接应用于杂交水稻育种计划，以提高产量。该项目将使用自然变异来识别赋予作物改良育种计划的生殖热应激抗性的位点，并描述这些性状。将筛选两个群体，i)一个“多样性小组”，包括来自不同地点和环境的800个全球代表性水稻品系，从3000基因组水稻计划中鉴定，ii)一个籼稻/粳稻染色体片段替代系群体，已知其对环境的育性反应具有多样性。这种材料将在田间和温室条件下表现为由于热胁迫而改变的生育力和花结构。将使用GWAS和渗入标记分析来确定相关的基因座。分子工具和转基因系将被用来剖析这些性状背后的机制。这将得到详细的显微镜和表达分析的支持。此外，转录组学方法将用于表征植物在热胁迫下繁殖过程中发生的分子变化，特别强调花粉发育过程中的绒毡层功能和程序性细胞死亡（PCD）。

Rice is the principal crop in China, comprising 36.9% of the world rice crop. Estimates suggest yield increases of 50% are needed by 2050 to ensure food security. The areas used to cultivate rice and timings of planting are driven by climatic conditions. Rice is cultivated across China; nevertheless the frequency of cropping and the areas where high yields can be realised are limited by temperature. Global climate warming negatively affects mean rice yield, but also variance in yield, leading to increased frequencies of low yields. Additionally, increased mean temperature negatively impacts on the length of vegetative growth and reproductive growth periods.Flower development is critical for plant breeding and seed production, and thus directly impacts on yield. Pollen formation is highly sensitive to temperature stress; high temperature stress during flowering therefore poses a serious threat to current and long-term crop yields. This is particularly the case since flowering and seed set typically occur during a single, transient stage of plant development, which unlike vegetative associated-stress, cannot be rescued if conditions subsequently improve. High temperatures reduce the number of flowering branches and therefore the number of flowers per plant, however abnormalities in pollen formation result in male sterility and thus failure of seed set. There is thus the potential for devastating yield losses if resilience to reproductive temperature stress is not developed, particularly given the rises in global temperature and the increased volatility of climatic conditions. Nevertheless there is considerable genetic variability in tolerance to high temperature between species and genotypes. Understanding how plants cope with heat stress during reproductive development offers the potential to identify genetic traits that can be manipulated and utilised to improve temperature tolerance in crops. This project will address these issues by developing germplasm with enhanced resilience to temperature stress. The programme will also provide detailed understanding of the molecular and cytological changes occurring during reproduction under heat stress, and the mechanisms conferring resilience to high temperatures. Developing such resilience will allow expansion of the areas used for rice cultivation, but also the timing and frequency of rice planting. This will lead to higher rice yields, but also to more resilient yields regardless of environmental fluctuations and global climate changes. Environmentally controlled male fertility also has major applications for developing materials for hybrid breeding. Knowledge and germplasm obtained from this project will therefore have direct application in hybrid rice breeding programmes for increased yield.The programme will use Natural Variation to identify loci conferring resistance to reproductive heat stress for breeding programmes for crop improvement, and to characterise these traits. Two populations will be screened, i) a "Diversity Panel" comprising 800 global representative rice lines derived from diverse locations and environments, identified from the 3000 Genome Rice Project and, ii) a population of indica/japonica chromosomal segment substitution lines, which has known diversity in fertility responses to environment. This material will be phenotyped in field and glasshouse conditions for altered fertility and floral architecture as a consequence of heat stress. GWAS and Introgression marker analysis will be used to identify the loci responsible. Molecular tools and transgenic lines will be used to dissect the mechanisms behind these traits. This will be supported by detailed microscopic and expression analysis. In addition transcriptomic approaches will be used to characterise the molecular changes occurring during plant reproduction under heat stress, specific emphasis will be paid to tapetum function and Programmed Cell Death (PCD) during pollen development.