Systems Biology of Plant Heterotrimeric G-protein Signaling in Overlapping Pathways Regulating Stomatal Closure

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This research will study a specialized plant cell type's response to adverse environmental conditions to provide new insights into how signaling components within living cells interact with each other to affect cell function. This specialized cell type, the guard cell, occurs in the epidermis, where pairs of guard cells enclose microscopic pores called stomata, through which plants take up CO2 (the substrate for photosynthesis) and, inevitably, lose water. Resultant improved understanding of the regulatory mechanisms by which guard cells respond to drought and atmospheric carbon dioxide levels can assist in development of crop varieties with greater yield under a range of growing conditions. General insights into biological networks gained in this project will improve understanding of dysregulated cell signaling, with broad implications for physiology, agriculture, and biotechnology. Personnel, including undergraduate researchers, will be cross-trained in emerging approaches in both experimental and computational biology. The principal investigators will develop a new course to introduce first year undergraduates to biological networks and other mathematical biology concepts and encourage STEM participation. Heterotrimeric G-proteins, composed of G-alpha subunits and G-beta-gamma dimers, comprise a ubiquitous signaling mechanism found in organisms as diverse as fungi, animals, and plants. This research will study G protein involvement in guard cell drought and CO2 signaling networks to address the fundamental question of whether and how G-alpha subunits compete for or partition their interaction with specific G-beta-gamma dimers. In plants, guard cells are the best understood single cell system of G protein regulation. In response to the hormone abscisic acid (ABA; an indicator of drought and other stresses), and to elevated concentrations of CO2, complex signaling networks are activated in guard cells that drive stomatal closure. This project will use genetic analyses to determine competition vs. partitioning of the four G-alpa subunits for the three Arabidopsis G-beta-gamma dimers during ABA and CO2 responses. The research will apply tests of protein-protein interaction to assess new candidate G protein interactors and to determine how G protein signaling interconnects with other known ABA and CO2 signaling components of guard cells. The project will develop new general reachability analysis and combinatorial logic methods to describe convergent or overlapping networks, and these methods will then be applied to the new experimental datasets obtained to create a new network model of the core components of G protein, ABA, and CO2 signaling. The new combinatorial logic methods for network construction developed will advance fundamental knowledge in systems biology: they will be applicable to directional signaling and genetic networks of any organism, and will enable a paradigm shift from assuming isolated linear pathways (e.g. as in classic epistasis analysis) to considering all network architectures consistent with a set of observations. Thus, the results from this research will have general implications for the common but complex phenomenon of cross-talk in biological systems.