The dominant late elongated hypocotyl (lhy) mutation of Arabidopsis disrupted circadian clock regulation of gene expression and leaf movements and caused flowering to occur independently of photoperiod. LHY was shown to encode a MBD DNA-binding protein. In wild-type plants, the LHY mRNA showed a circadian pattern of expression with a peak around dawn but in the mutant was expressed constantly at high levels. Increased LHY expression from a transgene caused the endogenous gene to be expressed at a constant level, suggesting that LHY was part of a feedback circuit that regulated its own expression. Thus, constant expression of LHY disrupts several distinct circadian rhythms in Arabidopsis, and LHY may be closely associated with the central oscillator of the circadian clock.
Bibliographical noteFunding Information:
This work was funded by a grant from the BBSRC (88/G07884) to I. A. C. I. A. C. was supported by a Warwick Research Fellowship. R. S. was supported by a BBSRC studentship. The lab of G. C. was supported by the BBSRC and Monsanto. The low-light video imaging facility at the University of Warwick was funded by the Gatsby foundation and the BBSRC. We wish to thank Joel Kreps for the CCR2 probe, Steve Kay for Arabidopsis plants carrying cab:luciferase gene fusions, and Elaine Tobin and Zhi-Yong Wang for sharing their data. We are grateful to Marty Straume for help with the statistical analysis, Kay Wheatley for helping harvest material, Kamal Swarup for technical assistance, Jonathan Clarke for help with the figures, as well as Andrew Millar, Malcolm Bennett, and Caroline Dean for their suggestions on the manuscript.