The gene network: This project focuses on a gene network that regulates plant responses to cytokinin, a key hormonal regulator of plant growth and development. The initial steps in cytokinin signaling are mediated by a 'two-component' system that transmits information from membrane to nucleus. The two-component system makes use of histidine kinases that act as cytokinin receptors, histidine-containing phosphotransfer proteins that transduce the initial signal, and response regulators that regulate the signal output. The transcriptional targets of this pathway as well as other outputs have yet to be determined. This project will delineate the network of genes and proteins regulated by two-component signaling elements of Arabidopsis. This two-component signaling network includes the transcription factors that control gene expression as well as interacting proteins that regulate other aspects of signal output. Project URL: www.bio.unc.edu/research/two-component/default.htm Functional characterization: Transcription factors will be characterized in terms of the genes that they regulate. Proteins will be characterized in terms of their protein-protein interactions within the signaling network. The physiological function of the network elements will be defined in terms of their role in regulating cytokinin responses as well as seed size, meristem function, vascular development, leaf and cotyledon morphology, metal ion homeostasis, and circadian rhythms. Sharing of results: Genomic information and tools generated will be made available to the research community through the web and through standard methods of publication in a timely fashion. Datasets of general interest, that are not made available through publication, will be deposited on the project web site within two years of their generation. Significance of work: These studies will define the circuitry by which the two-component gene network acts to alter plant growth and development. In addition, these studies will reveal connections between this pathway and other cellular networks. Determining how this integration is achieved will contribute to an understanding of signaling networks in plants and will serve as a model for examining other interactions within the plant cell. The techniques and tools developed during the course of these studies will assist gene studies in Arabidopsis and in other plant species. Broader impact: Results from the project will benefit society through the understanding of a critical gene network that regulates multiple traits of agronomic importance. Elucidation of these roles will provide avenues to modify such agriculturally relevant traits such as senescence, plant transformation, grain yield and filling, and patterns of growth and development. The plant research community will benefit by the optimization of novel research techniques and the development of new community resources. The proposed research will enhance the infrastructure of research and education by providing hands-on training for undergraduate students, graduate students, and post-doctoral researchers within the PIs' labs. In addition, the PIs will partner will local groups to assist in the creation and maintenance of programs aimed at fostering science education in grades K-12.
The purpose of this project was to characterize how a particular type of signaling pathway controls plant growth and development. The 'two-component' signaling pathways on which this study focused are evolutionarily ancient and are the primary means by which bacteria sense and respond to environmental stimuli. These pathways are comprised of a number of distinct elements, namely histidine kinases, response regulators and in the case of phosphorelays, histidine phosphotransfer proteins. Genes encoding similar proteins to each of these elements have been identified in plants and functional analysis indicates that two-component signaling elements play essential roles in plant growth and development. Significantly, two-component pathways control how plants perceive and respond to cytokinin, a plant hormone that regulates such agriculturally relevant traits as senescence, grain yield and filling, patterns of growth and development, and the interactions of plant hosts with symbiotic and pathogenic organisms. As a result of our studies, we identified and characterized genes and proteins regulated by these two-component elements in plants. The first objective of this study was to identify components of the transcriptional network regulated by the two-component signaling pathway. For this purpose, we successfully characterized changes in gene expression controlled by the pathway as well as identified key downstream transcription factors that control gene expression. The second objective of this study was to identify proteins that physically interact with elements of the two-component pathway. For this purpose, we successfully identified proteins that interact with activated forms of the response regulators. The third objective of this study was to functionally characterize genes and proteins identified in this study using genetic approaches. Here we successfully linked targets of the two-component signaling pathway to the regulation of chloroplast development, light responses, seed size, senescence, and stem cell maintenance. Results from this research have benefited society through the development of a systems level understanding of a critical gene network that regulates multiple traits of agronomic importance. The plant research community has benefited by the optimization of experimental techniques and the development of new community resources such as mutants that control key aspects of plant growth and development. The research and education infrastructure has benefited by hands-on training for undergraduate students, graduate students, and post-doctoral researchers. In addition, the PIs partnered with local groups to assist in the creation and maintenance of programs to improve science education in grades K-12.
