Coordinated Photoreceptor Engineering for Improved Biomass Production

A key challenge for plant biologists has been to increase plant yield by altering photosynthetic productivity to secure food, energy and environmental sustainability. Phototropin receptor kinases (phot1 and phot2) play an important role in this regard by coordinating multiple light-capturing processes. These include phototropism, chloroplast movements, leaf positioning, leaf expansion and stomatal opening all of which influence a plant's photosynthetic competence by improving the efficiency of light capture, reducing photodamage, and regulating gas exchange between leaves and the atmosphere. However, little effort has been made to target these pathways for improving biomass production.

We have recently shown that targeted engineering can be used successfully to modify the light-sensing properties of the phototropins and increase their sensitivity to light. Plants with these engineered photoreceptors exhibit more rapid and robust chloroplast movement responses and improved leaf positioning and expansion, leading to over 2-fold increases biomass accumulation under light-limiting conditions. These findings demonstrate the feasibility of engineering photoreceptors for improved plant growth and offer additional opportunities for enhancing plant yield through increases in photosynthetic competence.

This proposal capitalises on these findings and will use a combinatorial protein engineering strategy to better synchronise the actions of the phototropins more effectively over a wider range of light conditions without causing detrimental high-light stress. Design principles for better synchronisation between phototropin receptors will be established first in Arabidopsis and extended to crops using barley as a model. Thus, a major outcome of this interlinked effort will be to establish a structural and functional blueprint for constructing engineered photoreceptors that will provide a non-transgenic, genome editing-based approach to coordinate stepwise enhancements in photosynthetic performance with an aim to increasing crop yield.

This work will concurrently 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. As our knowledge of phototropin receptor signalling is still far complete, this proposal will also exploit the availability of a novel desensitised photoreceptor mutant background, identified from our phototropin engineering work, to identify new components of phototropin signalling through genetic suppressor screening. Together, the fundamental and applied aspects of this research will expand our understanding of phototropin receptor function and harness the ability to fine tune their action as a bona fide means to modulate yield for agronomic gain.

The ability to enhance photosynthetic capacity remains a recognised bottleneck to improving plant productivity. Phototropin receptor kinases (phot1 and phot2) play an important role in this regard as they coordinate multiple light-capturing processes that serve to maximise photosynthetic efficiency and promote growth. However, little effort has been made to target these pathways for improved biomass production. Our aims are (1) to optimise photocycle engineering of phot1 and phot2 in Arabidopsis with the goal of better synchronising their activities for gains in photosynthetic performance over a wider range of light conditions (2) apply these design principles to barley (Hordeum vulgrae) to increase productivity (3) establish a structural and functional blueprint for altering phot action that will be widely applicable across plant species and (4) capitalise on our photoreceptor engineering progress by using a novel, desensitised phot mutant background for genetic suppressor screening to identify new signalling components. This proposal integrates both fundamental and applied research that will expand our understanding of phototropin receptor kinase signalling and harness key optogenetic principles (tuning optical sensitivity for gain of function) to establish photoreceptor engineering as a bona fide means to modulate yield for agronomic gain. It builds on our recent success with improving biomass production in Arabidopsis by targeting phototropin receptors for optogenetic manipulation. The proposal draws on established methodologies to expand the array of phototropin variants with altered photochemical properties and identify the most promising of these prior to their use in Arabidopsis and barley. Given the high degree of sequence conservation between higher plant phototropins, the design principles established here should extend to other agronomically important plant species and further expand the array of phototropin-based modules for optogenetic applications.

This proposal combines practical and fundamental research that is central to concepts emerging from the fields of plant photobiology and optogenetics. The research will stimulate new thinking around ways to improve crop yield and offers new strategies to manipulate plant biomass through alterations in photosynthetic performance. The research therefore has potential to create a new engineering framework for crop improvement that could, in the long-term, benefit farmers, consumers and the environment and contribute to the economic competitiveness of the UK. Commercial organisations interested in implementing new approaches to manipulate plant growth, particularly by altering processes associated with regulating photosynthetic efficiency will also benefit in the longer term. Likewise, these organisations together with fundamental researcher will benefit from the design principles for fine tuning the action of LOV-based optogenetic tools. Additional impact is proposed through summer studentships to develop and implement outreach resources designed to engage the general public and school pupils in key concepts of photobiology, plant science and sustainability. Likewise, 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 and training of the staff will also benefit directly from the collaborative and inter-disciplinary nature of the project. Hence, the research will feed directly into higher education training programmes. Finally, the research will contribute to UK competitiveness and quality of life through agro-industrial applications. The PI and Co-Is have established links with industrial/technology transfer partners and research institutes to take advantage of development arising from the research.