Regulatory mechanisms of plant heterotrimeric G-protein signaling

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Plants respond to a variety of internal cues and external signals by employing multiple protein signaling complexes, which facilitate changes in plant physiology and environmental adaptation to optimize growth and development. Heterotrimeric GTP-binding proteins (G-proteins) are a class of proteins that have emerged as key regulators of a multitude of plant signaling pathways. These proteins are currently a focus of intense research due to their involvement in modulation of many agronomically important traits such as seed yield, plant defense responses, symbiosis and nitrogen use efficiency. The mechanistic details of how a small number of proteins regulate a multitude of signaling processes remain largely unknown. This research focuses on the regulatory mechanisms of G-proteins and will address some of the unique features of plant G-protein signaling, which remain undiscovered to date. Successful completion of this research will not only fill major gaps in our knowledge of plant G-protein signaling mechanisms, but will also build a foundation for further targeted studies in other economically important plants, where detailed mechanistic studies are currently not possible. Therefore, in addition to advancing the basic understanding in the field, this study may also apply broadly to some of the problems that challenge the world today, such as generating higher yield with limited resources and unfavorable environments. The work will involve training of a technician and a postdoctoral scientist in multidisciplinary approaches, as well as mentoring of undergraduate students. The research will also help promote an understanding of plant science to high school students and the general public via a series of hands on experiments and interactive presentations.Naturally occurring or engineered changes in the level of G-proteins cause profound effects on plant architecture, abiotic stress responses and yield potential, making elucidation of their underlying signaling mechanisms a high priority. The principal investigator has shown that the regulator of G-protein signaling (RGS) protein and a phospholipase D (PLDalpha1) protein act in a double negative loop to precisely control the level of active G-alpha protein in plant cells. The research will now focus on predicting and validating specific G-protein regulatory circuits using biochemical modeling and mutant response assays. Evaluation of the ancestral versus derived states of the G-protein regulatory modes will also be investigated by comparative evolutionary and genetic analyses. This research seeks to answer important questions related to plant G-protein regulatory mechanisms such as, (i) how is the plant G-protein cycle regulated, especially in the context of its unusual biochemical properties? (ii) how is the specificity of response regulation achieved despite a paucity of core components? (iii) how the activation/deactivation balance of G-alpha protein cycle is controlled in the absence of canonical G-Protein-Coupled Receptors in plants? (iv) why is the loss of a key regulatory protein (e.g. RGS protein) tolerated in a subset of plant species, even though it acts as an important regulator of the G-protein cycle in plants that possess it? and (v) what might replace RGS protein function in plants that lack it? Successful completion of this research is expected to not only shed light on G-protein signaling in plants, but to uncover additional, perhaps novel signaling and regulatory pathways in other eukaryotes that have been obscured until now due to the complexity of interactions.