Plant calcium-dependent protein kinases (CDPKs) have dual functions as calcium sensors and effectors, and are thought to be involved in multiple cellular responses to external and internal stimuli. However, their precise physiological functions remain elusive. Using a protoplast based functional genomics approach and RNA interference based reverse genetics, a novel function of two Arabidopsis CDPKs in auxin signaling was discovered, providing the first molecular evidence connecting Ca2+ signaling to the action of auxin. A CDPK double knockout mutant shows severe meristem defects, repression of several key meristem regulators, and exhibits abnormal growth throughout the plant life cycle. Based on these results, it is hypothesized that these two CDPKs represent a "missing link" between auxin and Ca2+ signaling, and developmental processes. The long-term goal of this research project is to understand the mechanisms and significance of the CDPK-mediated auxin signal transduction pathway. The data will show that a rapid movement of CDPK from the plasma membrane to the cytosol upon auxin stimulation is a crucial step for CDPK-dependent auxin signaling. The objective of this project is to identify and characterize cellular mechanisms controlling auxin-dependent CDPK translocation. The proposed experiments will use functional assays with an auxin-responsive reporter in both protoplasts and seedlings, combined with fluorescent-protein based bio-imaging to establish if CDPK-mediated auxin signaling involves protein lipid modification, phosphorylation, vesicle trafficking, and/or cytoskeleton remodeling.
