Engineering Blue Light Responses to Break the Carbon Water Trade Off and Approaches for Climate Resilient Plant Improvement

Plant productivity under climate change requires optimization of photosynthetic carbon assimilation while minimizing transpirational water loss, which is a fundamental physiological constraint governed by biophysical principles. This constraint arises because the steep leaf-air water vapor gradient, combined with the inherently faster diffusion coefficient of H₂O relative to CO₂, creates an inevitable trade off, whereby under typical condition, hundreds of water molecules are transpired for each CO₂ molecule assimilated during photosynthesis, particularly in C₃ species where the biochemical limitations of RuBisCO enzyme necessitate higher stomatal conductance to maintain adequate CO₂ supply for carboxylation reactions. This thesis investigates blue light signalling pathways as engineering targets for breaking this carbon-water tradeoff by examining regulatory mechanisms from photoreceptor-mediated signal transduction to whole plant level performance under dynamic environmental conditions. Novel large scale Imaging frameworks were developed to quantify guard cells patterning and its implications of spatial heterogeneity on the carbon water tradeoff which is previously inaccessible with conventional approaches (Chapter 3). The manipulation of spectral irradiance during development and induced hierarchical physiological modifications that enhance photosynthesis differentially across distinct temporal scales was explored in Chapter 4. A high throughput gas exchange protocol capable of collecting large amounts of data using a randomized unbiased algorithm was developed, and insights from this dataset led to the design of novel targeted spectral delivery strategies taking advantage of anatomical asymmetries to enhance photosynthetic efficiency, which resulted successfully in increasing daily CO₂ assimilation by 8.2 ± 1.3% while minimizing energy input through a periodic blue light pulsed system (Chapter 5). Following this, we explored genetically modified plants and discovered blue light driven compensatory mechanisms responding to genetically induced anatomical constraints (Chapter 6). We then engineered molecular enhancement through guard cell specific H⁺-ATPase overexpression and demonstrated reduced photosynthetic transition penalties from 17.3% to 6.9% under a novel naturalistic fluctuating light program developed as another methodological contribution in this thesis (Chapter 7). These integrated findings and methods developed thus provide engineering pathways and validation methodologies for developing future crops with enhanced resource use efficiency under variable environments in future climate scenarios.