Shedding light on clock controlled cab gene transcription in higher plants.

Research from several laboratories has revealed that the circadian clock regulates the transcription of many higher plant genes. Amongst the most well characterized of these genes are those that encode the chlorophyll a/b binding (Cab) proteins of the light harvesting complexes of photosystem II. Analysis of cab gene expression in both etiolated and green plants reveals a complex interaction between phytochrome(s) and the circadian clock, in which phytochrome appears to regulate the level of cab transcription and the circadian clock regulates the phase. The development of a non-invasive assay for cab transcription based on firefly luciferase expression in transgenic plants has not only made it possible to analyze clock regulated transcription in living plants, but also provides a means to screen for clock mutants in Arabidopsis.