Circadian Clock inArabidopsis thalianaDetermines Flower Opening Time Early in the Morning and Dominantly Closes Early in the Afternoon

Abstract

Many plant species exhibit diurnal flower opening and closing, which is an adaptation influenced by the lifestyle of pollinators and herbivores. However, it remains unclear how these temporal floral movements are modulated. To clarify the role of the circadian clock in flower movement, we examined temporal floral movements in Arabidopsis thaliana. Wild-type (accessions; Col-0, Ler-0, and Ws-4) flowers opened between 0.7 to 1.4 h in a 16 h light period and closed between 7.5 to 8.3 h in a diurnal light period. In the arrhythmic mutants pcl1-1 and prr975, the former flowers closed slowly and imperfectly, and the latter ones never closed. Under continuous light conditions, new flowers emerged and opened within the 23–26 h window in the wild-type, but the flowers in pcl1-1 and prr975 developed straight petals, whose curvatures were severely small. Anti-phasic circadian gene expression of CIRCADIAN CLOCK ASSOCIATED 1 (CCA1), LATE ELONGATED HYPOCOTYLE 1 (LHY1) and TIMING OF CAB EXPRESSION 1 (TOC1) occurred in wild-type flowers, but non-rhythmic expression was observed in pcl1-1 and prr975 mutants. Focusing on excised petals, bioluminescence monitoring revealed rhythmic promoter activities of genes expressed (CCA1 and PHYTOCLOCK 1/LUX ARRHYTHMO, PCL1/LUX) in the morning and evening, respectively. These results suggest that the clock induces flower opening redundantly with unknown light-sensing pathways. In contrast, flower closing is completely dependent on clock control. These findings will lead to further exploration of the molecular mechanisms and evolutionary diversity of timing in flower opening and closing.

Spatially specific mechanisms and functions of the plant circadian clock

“…We now describe recent progress in revealing the mechanisms underlying spatially specific functions of the circadian clock in plants. The clock has been shown to modulate a whole host of processes across the plant, including photosynthesis ( Dodd et al, 2005 ), senescence ( Song et al, 2018 ), leaf movement ( Kong et al, 2020 ), flower opening ( Muroya et al, 2021 ), and lateral root development ( Voß et al, 2015 ; see Figure 2 ). We will focus on recent interesting findings concerning clock control of growth and cell division, the role of clock components in temperature perception, and the role of the clock in modulating inter-species interactions.…”

“…The clock coordinates biological processes across the plant, in individual organs, tissues, and cell types. These include senescence ( Song et al, 2018 ), stomatal opening, photosynthesis ( Dodd et al, 2005 ) and rhythmic movement in leaves ( Kong et al, 2020 ), lateral root development ( Voß et al, 2015 ), root exudate composition ( Lu et al, 2021 ), and CS integrity in roots ( Durr et al, 2021 ), as well as flowering ( Hicks et al, 2001 ) and flower opening ( Muroya et al, 2021 ). Root-specific clock functions can also feed into microbiome composition ( Durr et al, 2021 ).…”

Chromosome number and phenotypic variations in hybrid populations of diploid and triploid in Hemerocallis

“…The fact that these rhythms are maintained under constant light or dark conditions suggests a circadian clock involvement. An analysis of the temporal oral movements in Arabidopsis thaliana shows that the circadian clock induces ower opening redundantly with unknown light-sensing pathways, and ower closing is completely dependent on clock control (Muroya et al 2021). Transcriptome sequencing analysis of the F1 populations of 'naomi ruth' and 'siyuehua' identi ed 23 key circadian clock genes that were differentially expressed in different daylilies.…”

The circadian clock controls temporal and spatial patterns of floral development in sunflower

“…In plants, the circadian system mediates the effects of day length during the transition from vegetative to reproductive growth, usually referred to as flowering time (Imaizumi and Kay, 2006). The circadian clock also regulates daily aspects of floral development, for example coordinating daily rhythms in scent emission and floral opening and closing with pollinator activity (Yon et al, 2017; Inoue et al, 2018; Muroya et al, 2021). In addition, the circadian clock is implicated in the uniform eastward orientation observed in mature sunflower plants; this eastward orientation was shown to enhance both male and female reproductive fitness (Atamian et al, 2016; Creux et al, 2021).…”