SAUR (Small Auxin Up RNA) proteins are a large family in all land plants. SAUR proteins can regulate activity of the plasma membrane H+-ATPase (proton pump), which energizes the plasma membrane for uptake of ions and metabolites. Growth hormones induce many SAUR genes, and these promote growth by the acid growth mechanism, whereby the proton pump acidifies the extracellular space both to loosen the cell wall and to promote uptake of solutes to maintain intracellular turgor. Other SAUR proteins act in guard cells to promote stomatal opening, which also depends on proton pump activity.
Loss of subsets of redundantly-acting SAUR genes can affect kinetics of growth or stomatal opening. Conversely, increased function of SAUR proteins can enhance growth dramatically and confer hypersensitivity to external cues such as gravity. We are working to understand the roles of SAUR proteins in cell expansion and in other aspects of physiology.
Some SAUR proteins promote growth after association with the plasma membrane through electrostatic interactions with anionic membrane lipids. We are also exploring how different domains or structural features of SAUR proteins mediate their localization and signaling functions, and how SAUR protein localization and activity are regulated.
Selected relevant publications:
Pereyra, M. E., Costigliolo Rojas, C., Jarrell, A. F., Hovland, A. S., Snipes, S. A., Nagpal, P., Alabadi, D., Blazquez, M. A., Gutierrez, R.A., Reed, J. W., Gray, W. M., Casal, J. J. 2023. PIF4 enhances the expression of SAUR genes to promote growth in response to nitrate. Proc Natl Acad Sci U S A 120: e2304513120. https://doi.org/10.1073/pnas.2304513120.
Nagpal P, Reeves PH, Wong JH, Armengot L, Chae K, Rieveschl NB, Trinidad B, Davidsdottir V, Jain P, Gray WM, Jaillais Y, Reed JW. SAUR63 stimulates cell growth at the plasma membrane. PLoS Genet. 2022 Sep 19;18(9):e1010375. https://journals.plos.org/plosgenetics/article?id=10.1371/journal.pgen.1010375
Wong, J. H., Klejchová, M., Snipes, S. A., Nagpal, P., Bak, G., Wang, B., Dunlap, S., Park, M. Y., Kunkel, E. N., Trinidad, B., Reed, J. W., Blatt, M. R., Gray, W. M. 2021. SAUR proteins and PP2C.D phosphatases regulate H+-ATPases and K+ channels to control stomatal movements. Plant Physiology 185(1): 256-273. doi:10.1093/plphys/kiaa023. https://academic.oup.com/plphys/article/185/1/256/5991409
Chae, K., Isaacs, C.G., Reeves, P.H., Maloney, G.S., Muday, G.K., Nagpal, P. and Reed, J.W. 2012. Arabidopsis Small Auxin Up RNA63 promotes hypocotyl and stamen filament elongation. Plant Journal 71:684-697. doi:10.1111/j.1365-313X.2012.05024.x. https://onlinelibrary.wiley.com/doi/full/10.1111/j.1365-313X.2012.05024.x