75 Integrating Membrane Transport with Male Gametophyte ... - TAIR

409 The circadian clock and light signaling converge on bHLH transcriptional regulators to
control rhythmic hypocotyl growth
Kazunari Nozue 1 , Stacey Harmer 1 , Michael Covington 1 , Paula Duek 2 , Severine Lorrain 2 , Christian Fankhauser 2 , Julin
Maloof 1
1
Section of Plant Biology, College of Biological Sciences, University of California, Davis, 2 Center for Integrative
Genomics, University of Lausanne, Switzerland
Most organisms use circadian oscillators to anticipate daily environmental changes, but little is known about how
circadian systems interact with normal diurnal signals (1). Strikingly, we find that the growth phase of Arabidopsis
hypocotyl in diurnal light conditions is shifted 8-12 hours relative to plants in continuous light, highlighting the
importance of clock/environment interactions. Expression profiling by Affimetrix ATH1 genome array and functional
analysis of various clock and photomorphogenic mutants revealed that two circadian regulated bHLH genes (PIF4 and
PIL6) function as intermediaries between the clock and light signaling. This interaction explains the observed diurnal
growth pattern and may serve as a paradigm for understanding intersections between endogenous and environmental
control of other processes.
(1) Nozue and Maloof (2006) Plant Cell and Environment 26:396-408
410 Structure-Function Analysis of a Small Molecule that Alters Auxin-mediated Gene
Expression in Arabidopsis thaliana
Sarah Miller 1 , Johann Bergholz 1 , Ronald Brisbois 2 , Rebecca Hoye 2 , Paul Overvoorde 3
1
Departments of Biology and Chemistry, Macalester College, St. Paul, MN 55105, 2 Department of Chemistry,
Macalester College, St. Paul, MN 55105, 3 Department of Biology, Macalester College, St. Paul, MN 55105
A combination of biochemical and molecular-genetic approaches has recently provided insights into aspects of auxinmediated
gene expression. Despite these advances, additional components that regulate auxin-controlled processes or
function in integrating multiple signaling pathways remain to be identified. Chemical genetics offers a powerful new
approach to understand plant hormone action. Identification of small molecules that perturb a signaling pathway can
lead to the isolation of the cellular targets of these compounds and their role in mediating signaling can be tested. This
approach has previously been used to identify a number of small molecules that alter auxin-inducible expression of the
BA3-GUS reporter gene (Armstrong et al., P.N.A.S. 101: 14978). As an outgrowth of efforts to provide interdisciplinary,
research-based opportunities for our undergraduate students, we have initiated a structure-function analysis of compound
A, a furyl acrylate ester of a thiadiazole heterocycle. Using the lab work of organic chemistry students as a starting
point, we have synthesized fourteen analogs of compound A, and are currently characterizing the effects that each
derivative has on auxin-regulated gene expression. Initially, the qualitative effect of each derivative is being determined
by examining changes in auxin-inducible expression of DR5-GUS or BA3-GUS reporter genes. Based on these initial
findings, quantitative real-time PCR will be used to define the effect of the derivatives on endogenous, auxin-modulated
gene expression. These molecules will then be used in plate-based assays to monitor the effects that the molecules have
on plant growth. Collectively, these data will provide insight into the active core component of compound A, which will
aid in efforts aimed at identifying the cellular target(s) of this molecule.