Role of the FEI/ACC pathway in regulating cell wall synthesis

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Plant cells are surrounded by a semi-rigid wall that is made primarily of chains of sugars. This plant cell wall provides structural support, defines the size and shape of cells, and provides a barrier to infection by pathogens. Plant cell walls are diverse and highly dynamic structures that respond to developmental and environmental cues. The main load-bearing component of plant cell walls is cellulose, which is made at the surface of cells by a large enzyme complex called cellulose synthase. In this project, it will be characterized how plants regulate how much cellulose they make. Prior work uncovered a pathway that controls this process by modulating the movement of the cellulose synthase complex to the cell surface. How this pathway works and how it interacts with the other elements in the cell to control cellulose synthase will be explored. Further, a novel signaling molecule, 1-aminocyclopropane-1-carboxylic acid (ACC), a precursor to ethylene, was found to act in this pathway. How ACC is perceived by cells and how it acts to modulate cellulose synthase function will be determined. The results from this work will provide insight into how plants regulate cell wall biosynthesis, which is crucial to understanding the development of plant form and other processes and is important for the burgeoning biofuels industry. This project will interact with programs designed to increase the representation of minorities in the sciences and several outreach programs that aim to increase the public understanding of plant science.A signaling pathway regulating cell wall synthesis has been defined that includes the FEI receptor-like kinases, SHOU4 (a novel transmembrane protein), and ACC acting as a signal independent of its conversion to ethylene. Prior results suggest that this pathway regulates CESA (cellulose synthase) function by modulating CESA trafficking to the plasma membrane. A diverse set of complementary experiments are proposed to further elucidate how this pathway regulates CESA function. A primary hypothesis that will be tested is that SHOU4 acts as a counter of CESA levels at the PM, with the complex generating a signal to negatively regulate CESA exocytosis to maintain optimal levels of cellulose biosynthesis. One key aspect of this model is the direct interaction of SHOU4 and CESA. This interaction will be further characterized, including elucidating the role of phosphorylation, potentially by the FEI kinases. Outputs of this complex will be identified by screening for proteins that interact with SHOU4. A second hypothesis that will be tested is that ACC negatively regulates CESA function. A genetic screen was used to identify elements involved in ACC perception. These mutant lines will be further characterized and the genes corresponding to these mutations will be cloned and characterized. These studies will increase the understanding of how cell wall biosynthesis is regulated, a process that is central to many aspects of plant growth and development and which is important for the burgeoning biofuels industry. Further, these studies will begin to define the mechanisms underlying ACC function in plants.This award was co-funded by the Physiological Mechanisms and Biomechanics Program in the Division of Integrative Organismal Systems and the Cellular Dynamics and Function Cluster in the Division of Molecular and Cellular Biosciences.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.