Journal Article

Circadian Expression of the <i>PpLhcb2</i> Gene Encoding a Major Light-Harvesting Chlorophyll <i>a/b</i>-Binding Protein in the Moss <i>Physcomitrella patens</i>

Setsuyuki Aoki, Seiji Kato, Kazuhiro Ichikawa and Masashi Shimizu

in Plant and Cell Physiology

Published on behalf of Japanese Society of Plant Physiologists

Volume 45, issue 1, pages 68-76
Published in print January 2004 | ISSN: 0032-0781
Published online January 2004 | e-ISSN: 1471-9053 | DOI: http://dx.doi.org/10.1093/pcp/pch006
Circadian Expression of the PpLhcb2 Gene Encoding a Major Light-Harvesting Chlorophyll a/b-Binding Protein in the Moss Physcomitrella patens

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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-h : 12-h 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 (PpLhcb1, PpLhcb2 and Zlab1). Moreover, transgenic reporter strains expressing luciferase under the control of the PpLhcb2 promoter showed bioluminescence patterns consistent with the Northern and RT-PCR data. At a higher concentration (4.5%) of glucose in the medium, the reporter strain showed self-sustained rhythms in DD, which was entrained to a differently phased 12 : 12LD, revealing a circadian regulation on the transcription. Kinetics of bioluminescent peaks in 12 : 12LD from gametophore was different to those from protonema, indicating a developmental regulation on PpLhcb2. Together, the regulatory link between the clock and Lhcb genes in P. patens shows characteristics that appear to differ from those in higher plants.

Keywords: Keywords: Circadian rhythm — Circadian clock — Light-harvesting chlorophyll a/b-binding protein — Physcomitrella patens.; Abbreviations: CBS, CCA1-binding site; DD, continuous dark; LD, light-dark cycle; LHC, light-harvesting chlorophyll a/b-binding; LL, continuous light; RT-PCR, reverse-transcription-polymerase chain reaction; ZT, zeitgeber time.

Journal Article.  7047 words.  Illustrated.

Subjects: Biochemistry ; Molecular and Cell Biology ; Plant Sciences and Forestry

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