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

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.

Food Security is a key global issue; the realisation that we will need to find food to meet a 50% population increase by 2050 provides major focus for strategies to increase agricultural production, but these cannot be at the expense of the environment. Pollen development is fundamental to plant fertilisation and is vital for the production of most of the food that we eat. The sensitivity of pollen to high temperature stress as prolonged or even by brief fluctuations in temperature, poses a significant threat to yields. This sensitivity is also a constraint to the locations where crops, e.g. rice, can be grown and also the timing of planting.
Understanding the impact of heat on inflorescence and pollen development and identifying resilient germplasm will provide a way to maximize fertility and thus maintaining crop yields in adverse environments.

The observations that the pathway of pollen development is highly conserved between dicots (Arabidopsis) and monocots (rice and barley) (Wilson and Zhang, 2009; Fernandez-Gomez and Wilson 2014) provides a valuable asset since the information obtained from individual species can be compared and used to facilitate developments in other crops. Outputs from this research provide opportunities for improving crop performance and help deliver food security, a strategic priority area supported by the BBSRC.

WHO WILL BENEFIT FROM THE RESEARCH? outputs will have direct impact in the field of developmental biology and will provide valuable information for biologists and biotechnologists and Plant Breeding Companies and Farmers.

The data will provide fundamental information on the pathways and processes of heat stress and will aid understanding of this problem, which is currently lacking. This is likely to have impact at all levels from specialised researchers, through to schools and textbooks.

The approaches being adopted for inflorescence architecture analysis will facilitate new technical developments linked to Phenotyping and Integrative Biology Research.
International collaborations will be extended and further developed. This provides a very efficient way of developing new resources, technical developments and providing opportunities for staff exchange, development and networking, which has massive benefits in the global context.

HOW WILL THEY BENEFIT?
-By generating germplasm and fundamental data on the pathways and processes of reproductive heat stress.
-By the development of tools (genes and linked markers) and resources (germplasm) for heat stress tolerance.
-By translating this information to other crops to provide heat tolerance.
-By understanding gene regulation mechanisms in the anther during pollen formation.
-By enabling basic research to be applied to male reproduction in crops. Data generated will be stored in according to UKAS guidelines and published in peer-reviewed journals.

IMPACT STRATEGY:Our work and the significance of our data will be imparted in a variety of ways:
-By publications in Internationally significant journals, the presentation of data at National and International Conferences and the filing of patents.
-Information flow via web sites. By workshops and discussion forums with colleagues in the UK and China to ensure transfer of ideas and adoption of best practices.
-Information and ideas linked to Plant Reproduction and GM will be imparted to Schools, by talks, visits and placements, providing opportunities to cultivate young people's interests in plant biology.

Timescales for Impact Development
Year 1: Discussion:potential outputs with researchers; discussions:breeding companies re germplasm development. Outreach activities to non-specialists.
Year 2: Dissemination of preliminary data to breeding companies; discussion re requirements for deployment into elite lines. Outreach.
Year 3: Discussions with potential users, Breeding Companies and Farmers. Dissemination of project data at International Rice research Conference.