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 feed-back circuit that regulated its own expression. Thus, constant LHY expression disrupts several distinct circadian rhythms in Arabidopsis, and LHY may be closely associated with the central oscillator of the circadian clock. Bios Scientific Publishers, Oxford. Biological timing in plants.
Plants present unique advantages for the study of circadian rhythms.
One is the variety of physiological processes that exhibit circadian rhythmicity. The use of novel luminescent reporters of gene expression and of calcium levels recently provided the first clues as to how the clock orchestrates many different activities in parallel. Signalling cascades for the transduction of light signals are the subject of intensive studies, making plants an unparalleled system for the dissection of phototransduction pathways for the entrainment of the clock to daily light-dark cycles. Finally, mutants with aberrant circadian rhythms have been isolated in the small weed Arabidopsis , that may lead to the identification of molecular cogs of the circadian oscillator in plants. Genetic analysis of the photoperiodic clock in Arabidopsis.