Plant and Cell Physiology Advance Access originally published online on March 8, 2006
Plant and Cell Physiology 2006 47(5):601-612; doi:10.1093/pcp/pcj027
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Conserved Expression Profiles of Circadian Clock-related Genes in Two Lemna Species Showing Long-day and Short-day Photoperiodic Flowering Responses
Department of Biological Science, Graduate School of Science, Nagoya University and CREST, Japan Science and Technology Corporation (JST), Furo-cho, Chikusa-ku, Nagoya, Aichi, 464-8602 Japan
* Corresponding author: E-mail, oyama{at}bio.nagoya-u.ac.jp; Fax, +81-52-789-2963.
The Lemna genus is a group of monocotyledonous plants with tiny, floating bodies. Lemna gibba G3 and L. paucicostata 6746 were once intensively analyzed for physiological timing systems of photoperiodic flowering and circadian rhythms since they showed obligatory and sensitive photoperiodic responses of a long-day and a short-day plant, respectively. We attempted to approach the divergence of biological timing systems at the molecular level using these plants. We first employed molecular techniques to study their circadian clock systems. We developed a convenient bioluminescent reporter system to monitor the circadian rhythms of Lemna plants. As in Arabidopsis, the Arabidopsis CCA1 promoter produced circadian expression in Lemna plants, though the phases and the sustainability of bioluminescence rhythms were somewhat diverged between them. Lemna homologs of the Arabidopsis clock-related genes LHY/CCA1, GI, ELF3 and PRRs were then isolated as candidates for clock-related genes in these plants. These genes showed rhythmic expression profiles that were basically similar to those of Arabidopsis under light–dark conditions. Results from co-transfection assays using the bioluminescence reporter and overexpression effectors suggested that the LHY and GI homologs of Lemna can function in the circadian clock system like the counterparts of Arabidopsis. All these results suggested that the frame of the circadian clock appeared to be conserved not only between the two Lemna plants but also between monocotyledons and dicotyledons. However, divergence of gene numbers and expression profiles for LHY/CCA1 homologs were found between Lemna, rice and Arabidopsis, suggesting that some modification of clock-related components occurred through their evolution.
The nucleotide sequences reported in this paper have been submitted to DDBJ under accession numbers AB210844–AB210847, AB210849–AB210852 and AB243681–AB243686.
(Received January 26, 2006; Accepted February 26, 2006)
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