He also held a position as Group Leader at the Friedrich Miescher Institute in Basel, Switzerland. Thus, light-regulated nucleocytoplasmic partitioning of phyA and phyB is an essential step in phytochrome signaling. Phytochromes have been shown to be the functional photoreceptors for entraining the circadian clock in higher plants. We found evidence that transcription of the phyB gene and the abundance of the phyB protein similar to canonical clock genes and proteins appear to be controlled by a circadian rhythm. Taken together these observations may indicate that phyB represents an ancestral oscillator mechanism or that phyB is a component of the central circadian clockwork in higher plants.
Recent data show, however, that phytochrome has another role during the life span of higher plants.
Accumulating evidence indicates that activation of phytochrome, apart from modulating gene expression of several plant genes directly, is also involved in setting or synchronizing the endogenous biological oscillator that further modulates gene expression. It has been shown that phytochrome and the circadian clock modulate the expression of various genes at the level of transcription. To date we have shown that expression of the Cab genes is regulated in a developmentally dependent manner by two circadian oscillators. These observations indicate that this photoreceptor is an essential component of the yet undefined plant circadian clock. The major goal of our work is to isolate a new type of Arabidopsis thaliana circadian clock mutant.