Download Two-component systems are the primary means by which bacteria

Project Summary
Senior Personnel:
PI: Joseph J. Kieber, Univ. North Carolina-Chapel Hill
Co-PI: Carol Parker, Univ. North Carolina-Chapel Hill
Co-PI: G. Eric Schaller, Dartmouth College
Co-PI: Dennis Mathews, Univ. New Hampshire
Intellectual Merit:
Two-component signaling systems make use of histidine kinases, response regulators, and
histidine-containing phosphotransfer proteins (HPts). These play essential roles in plant signal
transduction, in particular cytokinin signaling where the initial steps are mediated by a twocomponent system of cytokinin receptors, HPt proteins, and type-B response regulators. The
type-B response regulators act as transcription factors to regulate gene expression, including that
of the type-A response regulators. The two-component system thus functions as a regulatory
circuit capable of transmitting information from membrane to nucleus, and is the only such
circuit for which all components including the signaling ligand is currently known in plants. The
transcriptional targets of this pathway as well as other outputs have yet to be determined. We
therefore propose to delineate the network of genes and proteins regulated by the two-component
signaling elements of Arabidopsis. The first objective is to identify and characterize components
of the transcriptional network initiated by the type-B response regulators, which will be
accomplished using microarray analysis, GR-fusions to transcription factors, and ChIP chip
approaches. The second objective is to identify components of the protein-protein interaction
network, which will be accomplished by using two-hybrid analysis, purifying protein complexes,
and RNA display technologies. The third objective is to functionally analyze the network
elements identified through the first two objectives. For this purpose, we will perform molecular
and physiological analysis of loss-of-function mutants, with a focus on traits that we have found
to be regulated by the two-component signaling pathway. These include known cytokinin
responses as well as seed size, red light responses, pathogen responses, metal ion homeostasis,
and male and female gametophytic development. These data will be incorporated into a database
so that the research community can easily view the interaction network. These studies will
illuminate the signaling network in which the two-component signaling elements function and
how they interact to control plant growth and development.
Broader impacts:
Results from the proposed research will benefit society through the development of a systems
level understanding of a critical gene network that regulates multiple traits of agronomic
importance. Previous work suggests that elucidation of these roles will provide avenues to
modify such agriculturally relevant traits such as senescence, disease resistance, transformation
of recalcitrant plant species, grain yield and filling, and patterns of growth and development. The
plant research community will be benefited by optimization of the techniques of ChIP-chip and
mRNA display, and development of new community resources including two-hybrid libraries.
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.