Modulation of copper deficiency responses by diurnal and circadian rhythms in Arabidopsis thaliana.

Ana Perea-García,Seth J Davis,Amanda M Davis,Sonia Mayo De Andrés,Amparo Andrés-Bordería,Peter Huijser,Lola Peñarrubia,Amparo Sanz

doi:10.1093/jxb/erv474

Abstract

Copper homeostasis under deficiency is regulated by the SQUAMOSA PROMOTER BINDING PROTEIN-LIKE7 (SPL7) transcription factor. The daily oscillating expression of two SPL7-dependent copper deficiency markers, COPPER TRANSPORTER (COPT2) and IRON SUPEROXIDE DISMUTASE (FSD1), has been followed by quantitative PCR and in promoter:LUCIFERASE transgenic plants. Both genes showed circadian and diurnal regulation. Under copper deficiency, their expression decreased drastically in continuous darkness. Accordingly, total copper content was slightly reduced in etiolated seedlings under copper deficiency. The expression of SPL7 and its targets COPT2 and FSD1 was differently regulated in various light signalling mutants. On the other hand, increased copper levels reduced the amplitude of nuclear circadian clock components, such as GIGANTEA (GI). The alteration of copper homeostasis in the COPT1 overexpression line and spl7 mutants also modified the amplitude of a classical clock output, namely the circadian oscillation of cotyledon movements. In the spl7 mutant, the period of the oscillation remained constant. These results suggest a feedback of copper transport on the circadian clock and the integration of rhythmic copper homeostasis into the central oscillator of plants.

Highlights

In higher plants, the transition metals copper (Cu) and iron (Fe) exhibit redox properties that make them suitable to function as essential cofactors at the electronic transport chains in chloroplasts and mitochondria
In order to determine the time required to perceive changes in the environmental levels of Cu in Arabidopsis seedlings, the gene expression kinetics of the metal deficiency markers COPT2 and FSD1 were evaluated in seedlings grown under 12 h light and temperature cycles (LDHC) and different Cu regimes: sufficiency (1/2 MS with 1 μM CuSO4) and severe deficiency (1/2 MS with 50 μM bathocuproinedisulphonic acid (BCS)) for 6 d, after which they were transferred to media under the opposite Cu condition (Fig. 1)
The seedlings grown under severe Cu deficiency and moved to the sufficiency condition showed a relative decrease in COPT2 (Fig. 1A) and FSD1 (Fig. 1B) expression

Summary

Introduction

The transition metals copper (Cu) and iron (Fe) exhibit redox properties that make them suitable to function as essential cofactors at the electronic transport chains in chloroplasts and mitochondria. The temporary regulation of metal homeostasis and its integration with diurnal and circadian cyclic processes is starting to be elucidated. While light signalling is the main factor influencing daily changes in gene expression, the self-sustainable circadian clock generates endogenous rhythms that persist under constant conditions (Bujdoso and Davis, 2013). One of the mechanisms of how the light signal is integrated in the clock is based on the interactions of the GIGANTEA (GI) protein with light, oxygen, or voltage (LOV) and F-box domain proteins that differentially regulate its stability throughout the day (Kim et al, 2007; Sawa et al, 2007). The interactions are triggered by blue light and stabilize GI, which contributes to amplified expression of the clock protein TIMING OF CAB EXPRESSION1 (TOC1), providing clock robustness (Kim et al, 2007)

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Results

Conclusion