Analyses and Identification of molecular mechanisms underlying Calcium-sensor function and priming in guard cells
Final Report Abstract
Carbon dioxide uptake and water transpiration in plants is tightly regulated via opening and closing of stomatal pores. Stomatal pores are formed by specialized epidermal cells, so called guard cells. In order to avoid excess water loss by transpiration, guard cells integrate environmental and hormone signals and utilize signaling networks that include calcium and reactive oxygen species (ROS) as secondary messengers, as well as Snf1-related protein kinases (SnRKs) and Calcium-dependent protein kinases (CDPKs). The drought hormone abscisic acid (ABA) has been shown to elevate intracellular calcium levels but also to prime/increase calcium sensitivity. Calcium sensitivity priming by ABA is impaired in cpk3cpk6 double mutant plants, indicating a role of these calcium binding kinases in the process. Additional layers of regulation in these CDPKs besides calcium binding, such as posttranslational modifications might provide a mechanism of how calcium sensitivity priming and specificity in calcium signaling is achieved. I have identified ABA dependent phosphorylation sites and biochemically characterized their role in calcium binding and kinase activity. Further experiments are performed to test these phosphorylation sites in a biological context in plants. In CO2-dependent stomatal closing, we could demonstrate that carbonic anhydrase-mediated catalysis is an important initial step in CO2-induced stomatal closure. Arabidopsis thaliana ß-ca1ß-ca4 double mutants were strongly impaired in CO2-dependetn stomatal regulation. In addition we have characterized an ABA-responsive suspension culture and quantified changes in abundance of 23000 mRNA transcripts and 1100 proteins in response to ABA in order to identify new components of stomatal regulation. Further genetic and biochemical analysis of these gene/proteins is necessary in order to place them into the stomatal network. Highlighted in Spiegel Online Wissenschaft: http://www.spiegel.de/wissenschaft/natur/0,1518,666872,00.html Highlighted in San Diego Union Tribune: http://www.signonsandiego.com/news/2009/dec/14/discovery-may-change-plants-makeup/
Publications
- Carbonic anhydrases are upstream regulators of CO2-controlled stomatal movements in guard cells. Nature Cell Biology 12: 87-93
Hu H, Boisson-Dernier A, Israelsson-Nordström M, Böhmer M, Xue S, Ries A, Godoski J, Kuhn JM, Schroeder JI
