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Distinct Light and Clock Modulation of Cytosolic Free Ca²⁺ Oscillations and Rhythmic CHLOROPHYLL A/B BINDING PROTEIN2 Promoter Activity in Arabidopsis^[W]

^a Department of Biological Sciences, Vanderbilt University, Nashville, Tennessee 37235
^b Department of Plant Sciences, University of Cambridge, Cambridge CB2 3EA, United Kingdom
^c Department of Plant Sciences, Montana State University, Bozeman, Montana 59717

⁴ Address correspondence to alex.webb{at}plantsci.cam.ac.uk.

Plants have circadian oscillations in the concentration of cytosolic free calcium ([Ca²⁺]_cyt). To dissect the circadian Ca²⁺-signaling network, we monitored circadian [Ca²⁺]_cyt oscillations under various light/dark conditions (including different spectra) in Arabidopsis thaliana wild type and photoreceptor and circadian clock mutants. Both red and blue light regulate circadian oscillations of [Ca²⁺]_cyt. Red light signaling is mediated by PHYTOCHROME B (PHYB). Blue light signaling occurs through the redundant action of CRYPTOCHROME1 (CRY1) and CRY2. Blue light also increases the basal level of [Ca²⁺]_cyt, and this response requires PHYB, CRY1, and CRY2. Light input into the oscillator controlling [Ca²⁺]_cyt rhythms is gated by EARLY FLOWERING3. Signals generated in the dark also regulate the circadian behavior of [Ca²⁺]_cyt. Oscillations of [Ca²⁺]_cyt and CHLOROPHYLL A/B BINDING PROTEIN2 (CAB2) promoter activity are dependent on the rhythmic expression of LATE ELONGATED HYPOCOTYL and CIRCADIAN CLOCK-ASSOCIATED1, but [Ca²⁺]_cyt and CAB2 promoter activity are uncoupled in the timing of cab1 (toc1-1) mutant but not in toc1-2. We suggest that the circadian oscillations of [Ca²⁺]_cyt and CAB2 promoter activity are regulated by distinct oscillators with similar components that are used in a different manner and that these oscillators may be located in different cell types in Arabidopsis.

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