Cytokinins are thought to play a central role in controlling plant growth and development. They are essential for cell division and organogenesis in tissue culture, they can influence chloroplast development, delay senescence in detached tissues, and cause outgrowth of lateral buds. Despite these impressive effects, little is known about how cytokinins act. The long-term research goal is to understand how the cytokinin signal is perceived and transduced in the plant. Two approaches will be used: (1) Arabidopsis thaliana cytokinin-insensitive mutants will be identified. Because many interesting mutations might be lethal, screening will be conducted so that lethal recessive mutations can be retrieved as heterozygotes. Obtaining such mutants will enable future cloning of a gene involved in the cytokinin-response pathway. (2) Regulation of gene expression by cytokinins will be analyzed. One of the most dramatic and accessible effects of cytokinins is their ability to overcome apical dominance and cause outgrowth of lateral buds. Genes whose expression is induced within 6 hours of cytokinin treatment of tomato lateral buds will be cloned. Whether cytokinins control gene transcription or post-transcriptional processes will be determined. These experiments will produce the tools necessary for identifying cellular factors that control gene expression in response to cytokinins.
