Coordinated Photoreceptor Engineering for Improved Biomass Production

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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.