Systems Biology Framework To Investigate Coupling of Active and Passive Mechanisms of Stomatal Regulation

102 pagesClimate change is increasing the intensity and frequency of abiotic stresses – temperature, atmospheric humidity, and ambient carbon dioxide levels on plant life, leading to negative impacts on crop productivity and ecosystem sustainability. Plants control the exchange of carbon and water vapor through the pores in the leaf surface called stomata. Existing hypotheses for understanding stomatal conductance are divided into two distinct hypothetical approaches: a tissue-scale hydraulic hypothesis and a single cell-based autonomous biochemical hypothesis. Even though both these mechanisms are coupled physiologically, the development of these approaches has remained disconnected and there remains an incomplete understanding of coupling between the two modes of regulation; this disconnect hinders our ability to pursue genetic, molecular biological, and biophysical interventions to influence the regulation of gas exchange. In this thesis, I introduce a transient, tissue-scale Hydropassive (HP) model, a single-cell Hydroactive (HA) framework, and bases for coupling the two to describe the dynamics of stomatal conductance at the leaf-scale. After a review of the literature on the biology of stomatal regulation and on these two classes of models, I employ the HP framework to dissect the blurred boundary of timescales between the HP and HA responses. I demonstrate the use of the HP framework to test hypotheses and guide the design of experiments that will help estimate the physiological parameters and aid experimentalists in confronting existing and on-going observations of water potential dynamics. With results from the HA framework, I propose that the switch-like behavior of a futile cycle operating in the zeroth order ultrasensitive regime could inform a decades-old question regarding the selective advantage in evolving the HA response and the robustness of guard cell autonomous stomatal regulation under increased water stress. With the development of this systems biology model, I aim to advance our understanding of the multi-scale processes that underpin water stress management in leaves. I propose specific future collaborative studies between experimentalists and modelers that will define targets for engineering of improved crop efficiency, resiliency, and productivity