Plant and Cell Physiology Advance Access published online on March 8, 2006
Plant and Cell Physiology, doi:10.1093/pcp/pcj027
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1 Department of Biological Science, Graduate School of Science, Nagoya University, Nagoya, Aichi, 464-8602, Japan; CREST, Japan Science and Technology Corporation (JST), Furo-cho, Chikusa-ku, Nagoya, Aichi, 464-8602, Japan
* To whom correspondence should be addressed. The Lemna genus is a group of monocotyledonous plants with tiny, floating bodies. L. 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 somehow diverged between them. Lemna homologues 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 the Arabidopsis under light-dark conditions. Results from cotransfection assays using the bioluminescence reporter and overexpression effectors suggested that the LHY and GI homologues 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 homologues were found between Lemna, rice and Arabidopsis, suggesting that some modification of clock-related components occurred through their evolution.
Received January 26, 2006
Accepted February 26, 2006
Regular Paper
Conserved Expression Profiles of Circadian Clock-Related Genes in Two Lemna Species Showing Long-Day- and Short-Day Photoperiodic Flowering Responses
Kumiko Miwa 1,
Masayuki Serikawa 1,
Sayaka Suzuki 1,
Takao Kondo 1,
and
Tokitaka Oyama 1 *
Tokitaka Oyama, E-mail: oyama{at}bio.nagoya-u.ac.jp
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