Abstract
Woody plants in boreal zone respond to short daylength in fall and induce an initial phase of cold acclimation. To accurately measure the daylength, plants have an endogenous mechanism called as "circadian clock". In Arabidopsis, it is thought that a central oscillator of the circadian clock consists of LHY/CCA1 and TOC1/PRR1, which form a transcriptional feedback loop. To elucidate involvement of the circadian clock system in the phase of cold acclimation in boreal woody plants, we determined full-length cDNA sequences, circadian expressions and genomic structures of LHY/CCA1- and TOC1/PRR1-like genes in a model tree, Populus nigra, and subsequently conducted phylogenetic analyses of these genes. We found that, in leaves, two LHY/CCA1-like genes were expressed in the morning phase and the TOC1-like gene was expressed in the evening phase, which is similar to those in Arabidopsis. Furthermore, our results suggest that two LHY/CCA1-like genes were paralogs of each other.
