UC San Diego

A complex signal transduction network operates in guard cells to regulate stomatal apertures. Though our understanding of this signaling network continues to deepen, many fundamental questions remain regarding the identities of the proteins and second messengers that function in the network and their roles. The work presented in this thesis describes important progress in our understanding of the components and mechanisms of the stomatal signaling network, in the reference plant Arabidopsis thaliana. This work is particularly focused on the role of calcium transients in stomatal signaling and on the signaling pathway regulated by carbon dioxide. Experiments were pursued to analyze calcium dynamics using time-lapse imaging of transgenic guard cells, and stomatal phenotypes using gas exchange and direct microscopic measurements of stomatal apertures. Findings from several studies are reported here. Two of these studies identified important new components in the CO2 signaling pathway. One suggests a role for calcium transients in stomatal responses to CO2 and identified the GCA2 gene as a regulator of CO2 responses. The second characterized a novel kinase, HT1, that mediates guard cell CO 2 responses. A third project revealed common features of the stomatal signaling pathways activated by pathogenic elicitors and by abscisic acid (ABA), a drought stress hormone, and provided new information about calcium transients produced in guard cells in the absence of applied stimuli. Other stomatal signaling advances to which I contributed are also included. The findings presented in this thesis represent a substantial advance in our understanding of stomatal guard cell signal transduction