Structural analysis of a unique K-dependent channel gate

Stomata are pores that mediate gaseous exchange across the impermeable surface of plant leaves. They open in the light to allow CO2 entry for photosynthesis, and they close to reduce water loss and prevent leaf drying in the dark and when atmospheric humidity is low. Stomata are at the centre of a crisis in water availability and crop production that is unfolding and will escalate as global demand, especially in agriculture, outstrips fresh water supplies. Thus stomata are an important target in efforts to enhance crop performance and resilience while reducing water demands. Stomatal movements are driven by solute and water transport across the membrane of the guard cells that surround the pore. Guard cells harbour ion channel proteins to facilitate solute transport, especially potassium ions (K+), for stomatal movements. One of these channels, GORK, is regulated by K+ outside to ensure outward K+ flux, regardless of the thermodynamic driving force on K+. Mike Blatt (MB) was first to identify this unique regulatory behaviour, now a widely-recognised as a feature of virtually all plant outward-rectifier K+ channels. We do not yet know how K+ outside regulates channel activity, but experiments and structural analyses highlight two domains of the GORK protein that are important and are highly conserved among this group of channels across angiosperm plants. We know also that it is possible to enhance stomatal movements, with the promise of improved plant resilience and biomass gains, by engineering these domains in the channel to alter its regulation by K+ outside. Establishing the mechanism of K+ regulation is clearly important to a fundamental understanding of these unique channels. It is set to establish a new model for channel gating that differs substantially from the canonical models; equally, it will inform future efforts to enhance stomatal function, crop yields and resilience. We are confident that our findings will guide further efforts work with to crops. Alignments of GORK show a high sequence conservation across the angiosperms within the relevant domains. Furthermore, studies to date indicate a much greater scope for enhancing stomatal responsiveness by manipulating channel K+-dependencies. Thus, we propose to resolve the underpinning molecular mechanism, both to expand our fundamental knowledge of the channels, providing training across a range of cutting-edge technologies, and to guide future work towards gains in crop efficiencies with benefits for producers, consumers, and the environment. Two immediate challenges present themselves. The first challenge is to fully resolve the sites internal to GORK that are responsible and to test their contributions to the mechanics of K+-dependent regulation of GORK. The second challenge is to resolve the consequences and most effective strategies in manipulating GORK regulation that will maximise biomass gains and reduce water use by the whole plant. We propose now to address these challenges. The research is for a greater understanding of a fundamental rule of life that will (1) resolve the internal mechanics of GORK channel K+ sensitivity, and (2) establish a strategic range of behaviours to inform bioengineering of the channel for enhanced biomass gains and water use efficiency.