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

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. Rhythmic movements of plant organs were documented already several centuries BC, but the first known experiments searching for the origin of such rhythms were conducted by the French astronomer de Mairan. Working with a sensitive plant (likely Mimosa pudica), he could show that leaves moving in day/night conditions continued to move in constant darkness. During the following centuries, experiments with what Linnaeus later termed "sleep movements" resulted in both the concept of the circadian clock and that of osmotic motors 1,2. These so called nyctinastic movements often occur in non-growing tissue and are reversible as in several legumes. The reversible movements involve osmotic motors in the pulvinus organ 3 , but rhythmic leaf movements can also be growth associated and thus non-reversible. Such rhythms are evident in the movement of leaves in tobacco and cotyledons in Arabidopsis thaliana 4,5. The irreversibility of this process is probably due to deposition of new cell wall material and decreased wall extensibility, but tissue expansion likely results from mechanisms in common with those in pulvinus tissue 6. Since the introduction of the concept of a circadian or endogenous biological clock great progress has been achieved in understanding the mechanisms behind such internal rhythms. In plants most of this work has been performed in the flowering plant Arabidopsis 7. A working model of the plant circadian clock comprises a self-sustaining oscillator with an approximately 24-hour rhythm resulting mainly from transcriptional and translational feedback loops 8. In short, the main components in such models are a set of single MYB domain transcription factors, a family of PSEUDO-RESPONSE REGULATORs (PRRs), and a few plant specific genes with unknown biochemical function. 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 9-13. A second sub-family of related MYB-like transcription factors including REVEILLE4 (RVE4), RVE6 and RVE8 has an opposite function, enhancing clock pace through the activation of several core clock genes 14,15. The family of PRR genes comprise five members in Arabidopsis: PRR1, PRR3, PRR5, PRR...

PIF-independent regulation of growth by an evening complex in the liverwort Marchantia polymorpha

“…It is well established that auxin affects growth in plants (see for example the reviews [ 40 , 41 ], and references therein), and we have previously shown that auxin levels in wild-type M . polymorpha gemmalings show a clear circadian rhythm in LL conditions [ 32 ]. However, in Mp lux ge lines, auxin levels are higher, arrhythmic and increasing with time in LL [ 32 ].…”

“…Among the non-vascular land plants, the liverwort Marchantia polymorpha has recently emerged as a model species with low genetic redundancy among regulatory genes, simplifying genetic approaches [ 27 ]. Many molecular tools are available for genome editing and loss- and gain-of-function analyses [ 28 – 31 ], as well as tools for studying growth and clock output [ 32 , 33 ].…”

“…We previously confirmed that the EC genes have a function in the M . polymorpha circadian clock by generating knock-down lines of Mp LUX and Mp ELF4-LIKE (Mp EFL ) using artificial micro-RNA’s (amiR’s) [ 34 , 35 ], as well as knock-out lines of Mp LUX using CRISPR/Cas9 [ 30 , 32 ]. However, outside flowering plants, a role for EC genes in the control of growth has not been established.…”

Abiotic stress through time

“…1c,d). Molecular studies of the liverwort Marchantia polymorpha revealed characteristics of a circadian oscillator, as gene expression and thallus movement were rhythmic under constant light (Lagercrantz et al ., 2020). However, they appear to have lost the CCA1/LHY/RVE homolog and instead possess a single RVE3,4,5,6,8‐like homolog (Linde et al ., 2017) (Fig.…”

Circadian and diel regulation of photosynthesis in the bryophyte Marchantia polymorpha

“…M. polymorpha is thought to have diverged from flowering plants about 400 million years ago (Delwiche and Cooper 2015, Kohchi et al 2021), with liverwort-like plants occurring earlier in the fossil record than other land plant forms such as vascular plants (Edwards et al 1995). M. polymorpha is a useful model to investigate questions concerning the evolution of circadian regulation because it has a circadian oscillator that shares some components with flowering plants (Lagercrantz et al 2021, Linde et al 2017), there is circadian regulation of a subset of the transcriptome and the position of its thallus lobes (Lagercrantz et al 2021, Lagercrantz et al 2020), and it can be used in experimental designs comparable to models such as Arabidopsis. Whilst circadian rhythms and some aspects of circadian clock structure have been identified in M. polymorpha , it is not yet known whether the regulation of photosynthesis represents a conserved output from its circadian system.…”