We are in the Department of Molecular, Cell and Developmental Biology at the University of California at Los Angeles.
The Tobin lab is combining a biochemical and molecular genetic approach to examine how circadian rhythms are generated in plants. We are employing the model organism Arabidopsis thaliana and are particularly interested in understanding the central oscillator that generates the rythyms of about 24 hours. We are also investigating the roles of post-transcriptional processes such as phosphorylation in maintaining the rythyms.
A transcription factor named CCA1 (CIRCADIAN CLOCK ASSOCIATED 1) interacts with a phytochrome regulatory region of a photosynthetic gene of Arabidopsis thaliana. CCA1 is of particular interest because it is involved in both phytochrome and circadian regulation. Overexpression of the protein abolishes many different kinds of circadian rhythms including gene expression, leaf movements, photoperiodic flowering, and rhythmic growth of the hypocotyl. It is part of a negative feedback loop that suppresses its own synthesis. In fact, our work has shown that it is almost certainly part of the circadian oscillator itself. Our current work aims to define exactly how it interacts with other proteins and how the functioning of the oscillator is regulated. We have found that phosphorylation of CCA1 by the protein kinase CK2 is one way in which the clock is regulated. Other proteins that can interact with CCA1 are currently being investigated. We are also interested in the molecular basis of the interaction of the phytochrome photoreceptors and circadian rhythms.