GENETIC-ANALYSIS OF OSMOTIC AND COLD STRESS SIGNAL-TRANSDUCTION IN ARABIDOPSIS - INTERACTIONS AND CONVERGENCE OF ABSCISIC ACID-DEPENDENT AND ABSCISIC ACID-INDEPENDENT PATHWAYS

To dissect genetically the complex network of osmotic and cold stress signaling, we constructed lines of Arabidopsis plants displaying biolu minescence in response to low temperature, drought, salinity, and the phytohormone abscisic acid (ABA). This was achieved by introducing int o Arabidopsis plants a chimeric gene construct consisting of the firef ly luciferase coding sequence (LUC) under the control of the stress-re sponsive RD29A promoter. LUC activity in the transgenic plants, as ass essed by using in vivo luminescence imaging, faithfully reports the ex pression of the endogenous RD29A gene. A large number of cos (for cons titutive expression of osmotically responsive genes), los (for tow exp ression of osmotically responsive genes), and hos (for high expression of osmotically responsive genes) mutants were identified by using a h igh-throughput luminescence imaging system. The los and hos mutants we re grouped into 14 classes according to defects in their responses to one or a combination of stress and ABA signals. Based on the classes o f mutants recovered, we propose a model for stress signaling in higher plants. Contrary to the current belief that ABA-dependent and ABA-ind ependent stress signaling pathways act in a parallel manner, our data reveal that these pathways cross-talk and converge to activate stress gene expression.