Miwa Kumiko, Serikawa Masayuki, Suzuki Sayaka, Kondo Takao, Oyama Tokitaka
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.
Plant Cell Physiol. 2006 May;47(5):601-12. doi: 10.1093/pcp/pcj027. Epub 2006 Mar 8.
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.
浮萍属是一类具有微小漂浮体的单子叶植物。由于浮萍（Lemna gibba G3）和少脉浮萍（L. paucicostata 6746）分别表现出长日植物和短日植物的强制性和敏感光周期反应，它们曾被深入分析用于光周期开花和昼夜节律的生理计时系统。我们试图利用这些植物在分子水平上探究生物计时系统的差异。我们首先采用分子技术研究它们的生物钟系统。我们开发了一种便捷的生物发光报告系统来监测浮萍植物的昼夜节律。与拟南芥一样，拟南芥CCA1启动子在浮萍植物中产生昼夜表达，尽管它们之间生物发光节律的相位和持续性有所不同。然后，分离出拟南芥生物钟相关基因LHY/CCA1、GI、ELF3和PRRs的浮萍同源基因，作为这些植物中生物钟相关基因的候选基因。在明暗条件下，这些基因表现出与拟南芥基本相似的节律性表达模式。使用生物发光报告基因和过表达效应子的共转染试验结果表明，浮萍的LHY和GI同源基因在生物钟系统中的功能与拟南芥的对应基因相似。所有这些结果表明，生物钟的框架似乎不仅在两种浮萍植物之间保守，而且在单子叶植物和双子叶植物之间也保守。然而，在浮萍、水稻和拟南芥之间发现了LHY/CCA1同源基因的基因数量和表达模式的差异，这表明生物钟相关成分在它们的进化过程中发生了一些改变。
