Nyctinastic thallus movement in the liverwort Marchantia polymorpha is regulated by a circadian clock

Ulf Lagercrantz,Anja Billhardt,D Magnus Eklund,Sabine N Rousku,Karin Ljung

doi:10.1038/s41598-020-65372-8

Abstract

The circadian clock coordinates an organism’s growth, development and physiology with environmental factors. One illuminating example is the rhythmic growth of hypocotyls and cotyledons in Arabidopsis thaliana. Such daily oscillations in leaf position are often referred to as sleep movements or nyctinasty. Here, we report that plantlets of the liverwort Marchantia polymorpha show analogous rhythmic movements of thallus lobes, and that the circadian clock controls this rhythm, with auxin a likely output pathway affecting these movements. The mechanisms of this circadian clock are partly conserved as compared to angiosperms, with homologs to the core clock genes PRR, RVE and TOC1 forming a core transcriptional feedback loop also in M. polymorpha.

Highlights

The circadian clock coordinates an organism’s growth, development and physiology with environmental factors
We found a significantly higher expression of MpPRR and a strongly dampened rhythm in the Mpluxge mutants compared to wild type (Fig. 3d; both G and genotype x time interaction (GxT) terms in ANOVA have P < 10−12), supporting a role for the M. polymorpha LUX gene in the control of the transcription of circadian clock genes
In angiosperms the circadian clock regulates a wide range of processes, including those affecting metabolism, growth, abiotic and biotic stress, and various photoperiodic responses (40 and references therein)

Summary

Introduction

The circadian clock coordinates an organism’s growth, development and physiology with environmental factors. We report that plantlets of the liverwort Marchantia polymorpha show analogous rhythmic movements of thallus lobes, and that the circadian clock controls this rhythm, with auxin a likely output pathway affecting these movements The mechanisms of this circadian clock are partly conserved as compared to angiosperms, with homologs to the core clock genes PRR, RVE and TOC1 forming a core transcriptional feedback loop in M. polymorpha. The reversible movements involve osmotic motors in the pulvinus organ[3], but rhythmic leaf movements can be growth associated and non-reversible Such rhythms are evident in the movement of leaves in tobacco and cotyledons in Arabidopsis thaliana[4,5]. The early morning phased genes CIRCADIAN CLOCK-ASSOCIATED 1 (CCA1) and LATE ELONGATED HYPOCOTYL (LHY) encode two MYB-like transcription factors that function mainly as repressors of day- and evening-phased genes[9,10,11,12,13]. Important components of the Arabidopsis circadian clock include ZEITLUPE (ZTL), an F-box protein, and GIGANTEA (GI), encoding a large protein with unclear biochemical function[27,28]

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Conclusion