Elucidating structure-function relationship and signaling mechanisms of the novel group III G gamma protein AGG3 in Arabidopsis

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Due to their sessile nature, plants continuously adjust their growth, development and productivity in accordance with their surroundings. They respond to environmental stresses (e.g. drought, cold temperatures), various pathogens, low or high nutrient availability, and interactions with other organisms by precise modification of underlying signaling pathways. Several proteins, many of which are present in all organisms, have evolved plant-specific structural features and functions to effectively address these challenges. One such group of proteins is the heterotrimeric G-protein family, which although present in all eukaryotes, has certain plant-specific components and features. This research seeks to discover the unique signaling pathways regulated by a novel, plant-specific Gγ protein, AGG3, of Arabidopsis. Results obtained from this research will help us understand how plants maintain their yield against environmental stresses. These results will have potential practical applications in the breeding or engineering of more productive crops with limited resources. The work will also involve the training of a postdoctoral researcher in a multidisciplinary field and mentoring of undergraduate students. The research will help promote an understanding of plant science to the high school students and general public thorough a series of hands on experiments and interactive presentations.Even though all eukaryotes possess heterotrimeric G-proteins and their overall signaling mechanisms are broadly conserved, plants have taken the 'core' G-protein system and rewired it to meet their needs. One novel component of the plant G-protein system is the newly discovered, higher plant-specific, type III (or Class C) Gγ protein, represented by AGG3 in Arabidopsis. Type III Gγ proteins have a modular architecture, with an N-terminal domain similar to canonical Gγ , fused with a large C-terminal extension (up to 3 times the length of Gγ domain) that contains up to 35% cysteine (Cys). The type III Gγ proteins are currently a focus of intense research due to their involvement in regulation of many agronomically important processes in plants, including seed yield, organ size regulation, abscisic acid (ABA)-dependent signaling and stress responses, and nitrogen use efficiency. The mode of action of these proteins remains largely unknown, and some unique mechanisms that are independent of the classic G-protein cycle are also proposed. This research therefore aims to determine the G-protein-dependent and -independent roles of AGG3, and elucidate its underlying signaling mechanisms; especially those operative during abiotic stress signaling. Genetic complementation of single and higher order mutants will be performed using specific domains of AGG3, followed by identification of its protein interaction network. These analyses will help define the role of AGG3 and its network elements in abiotic stress signaling pathways and how it is related to its ability to control yield.