Overexpression of a <i>CO</i> homologue disrupts the rhythmic expression of clock gene <i>LgLHYH1</i> in <i>Lemna gibba</i>

Abstract

In plants, the circadian clock is involved in the regulation of various physiological phenomena. The Arabidopsis CONSTANS gene (AtCO), a central component in photoperiodic flowering, as well as the CONSTANS-LIKE 1 gene (AtCOL1), which has been suggested to be involved in the light input pathway, belong to the CONSTANS-LIKE gene family (COL family). To investigate the function of the COL family in the circadian system, we characterized CO homologues in two Lemna plant species (LgCOH1 in L. gibba G3 and LaCOH1 in L. aequinoctialis 6746). The expression of LgCOH1 was upregulated by light, showing diurnal rhythmic expression with peak expression during daytime. We examined the effect of LgCOH1 overexpression (LgCOH1-ox) on a circadian bioluminescent reporter. LgCOH1-ox damped the circadian bioluminescence rhythm, suggesting that it disturbed the circadian system. The overproduction of the N-terminal region including the zinc finger regions, or the C-terminal region including the CCT domain of LgCOH1 damped the circadian bioluminescence rhythm, suggesting that both regions were involved in the phenotypic abnormalities found in the full-length LgCOH1-ox mutant. The overexpression of AtCO also damped the circadian bioluminescence rhythm in our co-transfection assay using Lemna plants, while its effect on the circadian rhythm was weaker than that of LgCOH1-ox. Based on these results, we suggest that some COL family genes may function in the regulation of the circadian system including the light input pathway.