Covington, Michael, F , Harmer, Stacey, L .
The circadian clock regulates auxin signaling in an organ-specific manner.
The circadian clock plays a pervasive role in the temporal regulation of plant physiology, environmental responsiveness, and development. In contrast, the phytohormone auxin plays a similarly far-reaching role in the spatial regulation of plant growth and development. Seventy years ago, Went and Thimann noted that plant sensitivity to auxin varied according to the time of day, an observation which they could not explain. We have found an explanation for this observation: the clock modulates transcriptional and growth responses to auxin. This finding, along with auxin’s distinct organ-specific roles in plant development, led us to study clock regulation of auxin signaling in different organs. Previous studies have demonstrated that clock-regulated genes have the same phase (time of peak expression) in different parts of the plant. We were, therefore, excited to find that the circadian clock controls auxin transcriptional responses in an organ-specific manner. In contrast to auxin-independent circadian reporters, the phase of circadian auxin signaling in cotyledons lags ~8 hrs behind that in shoot apices/hypocotyls. Furthermore, the clock controls sensitivity to exogenous auxin such that the window of maximum response differs by ~8 hrs between these two regions. In contrast to aerial portions of the plant, auxin signaling in the roots is not circadian regulated. Likewise, preliminary findings suggest that the clock modulates gravitropic responses in the shoot, but not in the roots. This complex relationship between the clock and auxin raises many interesting questions about how and why the circadian clock differentially regulates the phase of physiological outputs.
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1 - University of California, Plant Biology, Life Sciences 1002, One Shields Avenue, Davis, CA, 95616, USA
2 - University of California, Plant Biology
Presentation Type: Plant Biology Abstract
Location: Exhibit Hall (Northeast, Southwest & Southeast)/Hilton
Date: Sunday, July 8th, 2007
Time: 8:00 AM