Abstract
Circadian clocks control the expression of Lhcb genes encoding the chlorophyll a/b-binding proteins broadly in seed plants. We show here that this regulation is also conserved in the primitive moss Physcomitrella patens. Northern blotting analyses revealed a robust daily oscillation of Lhcb mRNA levels in protonema cells in 12-hr:12-hr light-dark cycles (12:12LD) that damped rapidly in continuous darkness (DD). In continuous light (LL), by contrast with typical profiles in higher plants, Lhcb mRNA levels only peaked during the first day and thereafter it showed constant levels. Reverse transcription (RT)-PCR analyses showed similar patterns of expression in LL for three distinct Lhcb genes. At a higher concentration (4.5%) of glucose in the medium, transgenic reporter strains expressing luciferase under the control of the PpLhcb2 promoter showed self-sustained bioluminescence rhythms in DD, which was entrained to a differently phased 12:12LD, revealing a circadian regulation on the transcription.
