The Circadian Clock in Annuals and Perennials Coordination of Growth with Environmental Rhythms

Since the first signs of life on planet earth, organisms have had to adapt to the daily changes between light and dark, and high and low temperatures. This has led to the evolution of an endogenous time keeper, known as the circadian clock. This biological timing system helps the organism to synchronize developmental and metabolic events to the most favorable time of the day. Such a mechanism is of considerable value to plants, since they in contrast to animals cannot change location when the environment becomes unfavorable. Thus is the ability to predict coming events of central importance in a plants life. This thesis is a study of the molecular machinery behind the clockwork in the small weed plant Arabidopsis thaliana as well as its close relative perennial; the woody species Populus. We have characterized a novel component of the circadian clock, EARLY BIRD (EBI). EBI is involved in transcriptional and translational regulation, via interaction with the known post-translational clock regulator ZEITLUPE (ZTL). In Populus, we describe the role of the circadian clock and its components with respect to entry and exit of dormancy and show that gene expression of the Populus LATE ELONATED HYPOCOTYL (LHY) genes are crucial importance for freezing tolerance and thereby survival at high latitudes. Furthermore, the input to the Populus clock is mediated via the phytochrome A (phyA) photoreceptor.