Collaborative Research: Deciphering the evolutionary plasticity of recycling complexes in plants

Plant growth and development is regulated by proteins in the plasma membrane. These include eproton ATPases, proteins required for formation of the cell plate during division and expansion of the cell wall, large families of transport proteins important in the uptake and transport of water and nutrients throughout the plant, and receptor proteins that sense environmental signals and mediate cellular and whole plant responses. The activity of many of these proteins is regulated through internalization and recycling. This collaborative project will characterize the cellular machinery that expedites recycling of proteins to the plasma membrane. The evolutionarily conserved Retriever complex recycles plasma membrane proteins in humans, but is not well characterized in plants. The team will take an evolutionary approach, together with unbiased proteomics and cell biology methods, to characterize the cellular functions and developmental roles of Retriever in two species representing developmentally and physiologically divergent land plant lineages, Arabidopsis thaliana and Physcomitrium patens, whose Retriever complexes are already known to differ. This work will reveal the cellular mechanisms that recycle and thereby control the activity of plasma membrane proteins in plants. Beyond the fundamental knowledge gained, this project will produce educational materials that illuminate the importance of plant growth and health for agriculture and resistance to abiotic and biotic stress. These modules will provide developing scientists with opportunities to explore authentic examples of real-world research through visual explanations of experimental approaches in plant biology. Retriever is critical for both polarized and diffuse growth of cells in A. thaliana and is required for polarized growth in P. patens. The project will use proximity labeling of the Retriever subunits VPS29, VPS26C and CCDC22 to contrast the core composition and associated proteins that form Retriever in these two evolutionary divergent plants. Using this comparative approach will identify both conserved and species-specific Retriever interacting proteins as well as novel plant proteins that function as the scaffolding COMMD complex in a bryophyte and an angiosperm. Interacting proteins that are conserved in both plant species will be prioritized and used to test the central hypothesis that Retriever and its interacting proteins have retained deeply conserved cellular functions that impact plant growth and development. These studies will also identify plasma membrane proteins that are recycled by Retriever in these two plant species and begin to define the evolutionary history of Retriever and associated regulatory proteins. Analysis of protein function in intact plants at the cellular and whole organism level will define the roles of Retriever-associated regulatory proteins and/or plasma membrane cargo in mediating growth in response to developmental and environmental signals and in regulating cell wall organization. These studies will establish direct relationships between Retriever-mediated endosomal trafficking, cell wall structure, and growth in intact plants. This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.