Abstract
Previous studies of plant circadian clock evolution have often relied on clock models and genes defined in Arabidopsis. These studies identified homologues with seemingly conserved function, as well as frequent gene loss. In the present study, we aimed to identify candidate clock genes in the liverwort Marchantia polymorpha using a more unbiased approach. To identify genes with circadian rhythm we sequenced the transcriptomes of gemmalings in a time series in constant light conditions. Subsequently, we performed functional studies using loss-of-function mutants and gene expression reporters. Among the genes displaying circadian rhythm, a homologue to the transcriptional co-repressor Arabidopsis DE-ETIOLATED1 showed high amplitude and morning phase. Because AtDET1 is arrhythmic and associated with the morning gene function of AtCCA1/LHY, that lack a homologue in liverworts, we functionally studied DET1 in M. polymorpha. We found that the circadian rhythm of MpDET1 expression is disrupted in loss-of-function mutants of core clock genes and putative evening-complex genes. MpDET1 knock-down in turn results in altered circadian rhythm of nyctinastic thallus movement and clock gene expression. We could not detect any effect of MpDET1 knock-down on circadian response to light, suggesting that MpDET1 has a yet unknown function in the M. polymorpha circadian clock.
Highlights
Diurnal rhythms in various biochemical and physiological processes are typical for most organisms, as an adaptation to the perpetual cycle of day and night
To obtain information on genes displaying circadian expression in constant light conditions (LL), we sequenced the transcriptomes of whole wild-type M. polymorpha gemmalings at eight time points over 2 d (Fig. 1a), using three experimental replicates
Our estimate for M. polymorpha is similar to those presented in comparable studies for other plant species for example maize (10%; Kahn et al, 2010), Arabidopsis (10%; Covington & Harmer, 2007) rice and poplar (8–13%; Filichkin et al, 2010)
Summary
Diurnal rhythms in various biochemical and physiological processes are typical for most organisms, as an adaptation to the perpetual cycle of day and night. Many of these rhythms persist in a constant environment without a day/night cycle. 24 h that stems from transcriptional and translational feedback loops (Harmer, 2009). Even though these mechanisms are typical for clocks in basically all organisms, the genes that are involved differ between taxa, supporting multiple origins of circadian clocks (Dunlap, 1999; Young & Kay, 2001; McClung, 2013). CIRCADIAN CLOCKASSOCIATED 1 (CCA1) and LATE ELONGATED
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