Different circadian oscillators control Ca2+ fluxes and Lhcb gene expression

Circadian biological clocks control many biological events, but the pathway s by which these events are controlled are largely unknown. Based on a mode l suggesting that cytosolic-free calcium levels control the expression of t he Lhcb gene in plants, we tested whether the circadian oscillation of free calcium is responsible for driving the rhythm of Lhcb expression. We found that these rhythms free-run with different periods in tobacco seedlings in constant conditions. Moreover, robust oscillations of Lhcb promoter activi ty continued in undifferentiated tobacco calli in the absence of Ca2+ oscil lations. Therefore, these two circadian rhythms are not linked hierarchical ly. These data provide evidence for separate circadian pacemakers controlli ng molecular events in plants.