Abstract
The rotation of the Earth entails changes in environmental conditions that pervasively influence an organism’s physiology and metabolism. An internal cellular mechanism known as the circadian clock acts as an internal timekeeper that is able to perceive the changes in environmental cues to generate 24-h rhythms in synchronization with daily and seasonal fluctuations. In plants, the circadian clock function is particularly important and regulates nearly every aspect of plant growth and development as well as proper responses to stresses. The circadian clock does not function in isolation but rather interconnects with an intricate network of different pathways, including those of phytohormones. Here, we describe the interplay of the circadian clock with a subset of hormones in Arabidopsis. The molecular components directly connecting the circadian and hormone pathways are described, highlighting the biological significance of such connections in the control of growth, development, fitness, and survival. We focus on the overlapping as well as contrasting circadian and hormonal functions that together provide a glimpse on how the Arabidopsis circadian system regulates hormone function in response to endogenous and exogenous cues. Examples of feedback regulation from hormone signaling to the clock are also discussed.
Highlights
The circadian clockwork relies on the integration of multiple components and regulatory mechanisms that results in 24-h biological oscillations [1,2]
Studies in other plant species are helping us understand the degree of conservation and how the clock has evolved during evolution [3,4]
A possible molecular connection between the clock and CK signaling was hinted in studies showing that the evening complex (EC) represses the CK-related genes ARR6, ARR7, CYTOKINE OXIDASE5, CYTOKININ RESPONSE FACTOR 4 (CRF4), and CRF5 [75]
Summary
The circadian clockwork relies on the integration of multiple components and regulatory mechanisms that results in 24-h biological oscillations [1,2]. That repressed of first components described to be part of the Arabidopsis oscillator included the LATE the evening-expressed pseudo response regulator (PRR) TIMING OF CAB EXPRESSION1/PSEUDO. The. CCA1 and LHY regulate other members of the PRR family including PRR9, PRR7, and PRR5 function of PRRs is alleviated through the activity of the evening complex (EC), which comprises [21]. The single MYB and clock-related component known as REVEILLE8/LHY CCA1 LIKE5 (RVE8/LCL5) promotes the expression of TOC1 and other clock genes through binding to their promoters [30,31,32]. The transcriptional activation by RVE8 involves the interaction with the co-activators NIGHT LIGHT-INDUCIBLE AND CLOCK-REGULATED GENES (LNKs), which form a protein complex to activate the transcription of the evening-expressed clock genes [33]. The mechanism by which RVE8 and LNKs activate circadian gene expression was recently identified and involves the recruitment of the transcriptional machinery to the evening-expressed loci to generate the rhythms in nascent RNAs [38]
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