PHOTORECEPTOR OPTIMISATION OF PLANT WATER USE

A changing climate coupled with increasing population and resource use is placing a greater strain on our ability to feed the world community. Crop productivity is dependent on water availability and predicted reductions in this resource could seriously impact our Food Security. We therefore need to develop crops with improved photosynthetic performance and reduced water use. A plants performance is determined by its ability to respond to environmental signals. Light is one of the most important signals for regulating plant growth and development. It is required not only for photosynthesis but also various other processes including seed germination, stem elongation and leaf development. Transforming a light signal (direction, quality and quantity) into a response is the role of plant photoreceptors and phytochrome B, a red/far-red photoreceptor, plays a major role in many of these responses. This includes balancing photosynthetic performance with the amount of water a plant uses. Plants defective in phyB, show a trade-off with significant improvements in their water use at the expense of reductions in their photosynthetic performance. Our work has shown that phyB regulates the development of stomata on the leaf surface. Stomata are the small pores found on the surface of leaves and they are critical regulators of plant gas exchange, balancing the uptake of carbon dioxide gas, which is required for photosynthesis, in exchange for water vapour. phyB signalling determines the number of stomata that develop on a leaf, which has a direct impact on plant water use and photosynthesis. A major outcome of this proposal will be to establish the role of a phyB signalling network in regulating this process through both tissue specific and inter-tissue signalling. Modulating this phyB signalling network presents a means of manipulating the trade-off between water use and photosynthesis to generate plants with improved performance.

Light has a major impact on plant growth and development regulating processes such as seed germination, stem elongation, leaf morphogenesis and development, including stomatal development. We have demonstrated that the red/far-red light photoreceptor, phytochrome B has a dominant role regulating stomatal development. Stomata are major regulators of plant water use and productivity and understanding their development is crucial to ensure our Food Security in a changing environment. phyB mutants not only show defects in stomatal development, but also significant improvements in water use, at the expense of net carbon assimilation. With new data, we propose a model that links signalling events in the epidermis with those in the mesophyll to determine stomatal development. The proposed network enables plants to discriminate impulsive light signals of short duration from more sustained light signals and prevents premature stomatal development. phyB is pivotal to this inter-tissue network and ensures that that plants efficiently conserve water in a changing light environment. To interrogate this model and provide novel mechanistic insights into how light signalling regulates plant water use we have three aims. To establish the role of phyB in regulating components of the network in both the epidermis and photosynthetic mesophyll tissues. We will then interrogate key components of the network to elucidate the mechanism by which light regulates stomatal development in the epidermis. Finally, we will use physiologically methods to determine whether manipulation of this pathway can uncouple the trade-off between water use and carbon assimilation in phyB mutants.

Who will benefit from this research?
This project is aimed at understanding the mechanism that regulate plant water use in response to light signals. The academic community will benefit through improved understanding of this research and this is discussed elsewhere in this proposal. The major beneficiaries outside of academia will primarily be staff employed on the project, business and industry, the farming community along with the general public and potentially the environment.

How might they benefit from this research?
The aims of this work is to understand how light signals balance plant water use and photosynthetic performance. This has the potential to lead to future translational research by altering water use in economically important plant species, with translation into wheat already initiated. A significant proportion of the UKs outdoor crops are rainfed (>90%) however, UK agriculture still uses over 130 Million tons of water annually for spray irrigation of plants. Seasonal water availability is predicted to be reduced across the UK over this century according to government reports (DEFRA, 2009). This will place a greater demand on UK water supplies and hence impact on UK business and industry in general. Therefore, the identification of genes and mechanisms that influence water use and productivity in commercial grain and bioenergy crops such as wheat, barley, miscanthus or coppiced willow will accelerate the generation of crops designed for improved performance in future environments. Such information will be valued by Agritech and Bioenergy companies as well as crop breeders who can generate new crop varieties through either enhanced breeding programs based on gene sequence data or through genetic modification (dependent on policy and demand). This in turn may impact on the UK Food and Drink Industry as, for example brewing and bread-making are reliant on grain-crops and by improving water use of such crops there is the potential benefit of ensuring sustainable future supplies of these grains, mitigating losses due to climate change (improved Food Security). As end users, farmers may potentially benefit from the development of such crop varieties at several levels with reduced costs associated with payments to water companies, abstraction of water from rivers and boreholes and construction of on farm reservoirs. This work also focuses on stomatal development and there is a growing body of research indicating that stomata have a key role to play in regulating plant-pathogen interactions. Reductions in stomatal number may therefore improve tolerance to a variety of pathogens which will be of major interest to the aforementioned groups. Engagement with these various groups will be achieved through displays at the Oxford Farming Conference, an event attended by industry, policy makers, farmers and academics and offers a means of meeting these potential beneficiaries and highlighting the research and its potential impact. Project Sunshine, the Plant Production and Protection (P3) project and the Grantham Centre for Sustainable Futures in Sheffield will also facilitate interaction with industry and policymakers through open days and networking events. The staff employed on this project will benefit from an excellent training environment and these skills will then be of significant value to both the academic and commercial sector. The public can recognise the link between light and photosynthesis and will therefore appreciate that plants have systems for differentiating between different light signals and altering their growth and development to maximise their performance. We will therefore utilise displays and talks during events such as the Sheffield Festival of Science and Engineering and University Open days to engage the wider public and highlight the significance of plant water use and food security.