The late elongated hypocotyl Mutation of Arabidopsis Disrupts Circadian Rhythms and the Photoperiodic Control of Flowering

Abstract 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 MYB 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.