Photoreceptor Engineering to Modulate Plant Growth

Light is critical for coordinating plant growth and development. Blue light (320-500 nm) in particular acts to regulate a wide range of responses that serve to promote growth. These processes include chloroplast relocation movements, leaf positioning and expansion, stomatal opening and phototropism, all of which influence a plant's photosynthetic competence by improving efficiency of light capture, reducing photodamage, and regulating gas exchange between leaves and the atmosphere. Collectively, these responses elicit dramatic effects on plant growth and are controlled by phototropin blue-light receptors. Therefore, manipulation of phototropin receptor activity offers additional opportunities to increase photosynthetic performance and promote growth under specific light conditions. Indeed, our recent results demonstrate the potential to alter plant growth through changes in phototropin reactivity. Hence, a major outcome of this work will be to establish a structural and functional blueprint for constructing engineered photoreceptors directed at optimising photosynthetic productivity under specific light conditions. This proposal therefore offers an additional approach to coordinate stepwise enhancements in photosynthetic performance with an aim to increasing yield that should ultimately offer new strategies to grow crops more efficiently. The work outlined in this proposal will also generate new photoreceptor components with tailored photochemical properties that will have utility in generating synthetic protein-based switches designed to regulate target cellular activities by light.

Increasing plant biomass has the potential to offer solutions for the food, energy, and environmental challenges of the future. Enhancing photosynthetic capacity and efficiency are recognised in this regard as bottlenecks to raising plant productivity. Recent engineering strategies have targeted diverse aspects of photosynthesis. However, an additional approach would be to target physiological processes that serve to optimise photosynthetic productivity. These include phototropism, leaf flattening and positioning, solar tracking, chloroplast relocation and stomatal opening, all of which are regulated by phototropin blue light receptors. Thus, engineering phototropin function has the potential to modulate plant growth through changes in photosynthetic efficiency. By using a directed evolution approach, we have identified key amino acid changes that markedly increase or decrease phototropin reactivity. This proposal focuses on harnessing these findings to fine-tune photoreceptor reactivity with an aim to modulate plant growth through changes in photosynthetic performance in Arabidopsis thaliana. Given the high degree of sequence conservation between higher plant phototropins, the design principles established here should extend to plant species important for producing sustainable food supplies and alternative fuel sources. This project is therefore of central importance to understanding how light is integrated to control a variety of responses that collectively promote plant growth and will ultimately provide new strategies to manipulate yield for agronomic gain. Knowledge gained from this work will also have relevance in the design of photosensory modules for emerging optogenetic applications.

Beneficiaries: Beneficiaries of the research will include: academic scientists interested in plant photobiology and plant biotechnology, synthetic biologists interested in the design of artificial photoreceptor systems, commercial organisations interested in developing new strategies to improve crop production, individuals (text books for teaching), and organisations involved in science communication to schools and to the wider public (e.g. Glasgow Science Centre). Phototropin research will also appeal to the general public who can relate to the early phototropism work of Charles Darwin and its impact on science and evolution.

Benefits: The impact of the research is derived from its relevance to understand how blue light coordinates a variety of processes that serve to optimise photosynthetic efficiency and promote plant growth and the potential relevance to crop improvement for agronomic gain. Phototropin blue light receptors elicit dramatic effects on plant growth by collectively regulating chloroplast relocation movements, leaf positioning and expansion, stomatal opening and phototropism, all of which influence a plant's photosynthetic competence by improving efficiency of light capture, reducing photodamage, and regulating gas exchange between leaves and the atmosphere. Thus, research on engineering phototropin function has the potential to generate new strategies to further modulate plant growth through changes in photosynthetic efficiency. Phototropin signalling pathways are also known to prime plant defence responses and potentiate pathogen resistance. Hence, the engineering strategies devised in this proposal could also prove useful towards improving pathogen tolerance. Phototropins are universal in higher plants. Therefore, this project has the potential, in the longer term, to create new avenues for crop improvement that could benefit farmers, consumers and the environment and contribute to the economic competitiveness of the UK. The staff assigned to the project will obtain knowledge and expertise that can be applied in related research fields or more widely in the commercial or public sectors. Career progression of the RA will also benefit directly from collaborative aspects of the research with Prof. Getzoff (The Scripps Research Institute, San Diego).

Activities: The project will be continually managed by the PI to engage potential beneficiaries. The PI will publish the research in high-impact scientific journals, write reviews and book chapters and inform the University Media Relations Office of research highlights. Discussions with relevant commercial organisations will be initiated when appropriate to promote exploitation. The PI will communicate the research to school and university students via visits and University open days, initiate discussions with the Glasgow Science Centre, and present lectures at national and international conferences, as well as within Universities throughout the UK. The PI's web site will be routinely updated to communicate the research to the general public.