Iron Is Involved in the Maintenance of Circadian Period Length in Arabidopsis

Yong-Yi Chen,Varanavasiappan Shanmugam,Lung-Jiun Shin,Chyi-Chuann Chen,Jing-Fen Wu,Kuo-Chen Yeh,Munkhtsetseg Tsednee,Shu-Hsing Wu,Ying Wang,Jing-Chi Lo

doi:10.1104/pp.112.212068

Yong-Yi Chen, Varanavasiappan Shanmugam + Show 8 more

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https://doi.org/10.1104/pp.112.212068

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Abstract

The homeostasis of iron (Fe) in plants is strictly regulated to maintain an optimal level for plant growth and development but not cause oxidative stress. About 30% of arable land is considered Fe deficient because of calcareous soil that renders Fe unavailable to plants. Under Fe-deficient conditions, Arabidopsis (Arabidopsis thaliana) shows retarded growth, disordered chloroplast development, and delayed flowering time. In this study, we explored the possible connection between Fe availability and the circadian clock in growth and development. Circadian period length in Arabidopsis was longer under Fe-deficient conditions, but the lengthened period was not regulated by the canonical Fe-deficiency signaling pathway involving nitric oxide. However, plants with impaired chloroplast function showed long circadian periods. Fe deficiency and impaired chloroplast function combined did not show additive effects on the circadian period, which suggests that plastid-to-nucleus retrograde signaling is involved in the lengthening of circadian period under Fe deficiency. Expression pattern analyses of the central oscillator genes in mutants defective in CIRCADIAN CLOCK ASSOCIATED1/LATE ELONGATED HYPOCOTYL or GIGANTEA demonstrated their requirement for Fe deficiency-induced long circadian period. In conclusion, Fe is involved in maintaining the period length of circadian rhythm, possibly by acting on specific central oscillators through a retrograde signaling pathway.

Highlights

The homeostasis of iron (Fe) in plants is strictly regulated to maintain an optimal level for plant growth and development but not cause oxidative stress
To confirm the effect of Fe deficiency on the expression of the central oscillator genes, quantitative reverse transcription (RT)-PCR was used to analyze the steady-state transcripts of CLOCK ASSOCIATED1 (CCA1), LATE ELONGATED HYPOCOTYL (LHY), PRR9, PSEUDO-RESPONSE REGULATOR7 (PRR7), PRR5, GI, TIMING OF CAB EXPRESSION1 (TOC1), and EARLY FLOWERING4 (ELF4)
The data showed long circadian periods under Fe deficiency (Fig. 2; Table I), and transcript levels of CCA1, LHY, PRR9, and PRR7 were reduced under Fe-deficient conditions in comparison with controls (Fig. 2)

Summary

Introduction

The homeostasis of iron (Fe) in plants is strictly regulated to maintain an optimal level for plant growth and development but not cause oxidative stress. Fe is involved in maintaining the period length of circadian rhythm, possibly by acting on specific central oscillators through a retrograde signaling pathway. Metals such as iron (Fe), copper (Cu), zinc (Zn), manganese (Mn), molybdenum, and nickel are essential for the various biological processes that govern plant growth and development (Marschner, 1995). The central feedback loop is composed of the morning-expressed genes CIRCADIAN CLOCK ASSOCIATED1 (CCA1) and LATE ELONGATED HYPOCOTYL (LHY) and the evening-expressed gene TIMING OF CAB EXPRESSION1 (TOC1; Schaffer et al, 1998; Wang and Tobin, 1998; Strayer et al, 2000; Alabadí et al, 2001). After receiving input signals in the form of environmental cues, the central oscillator of the Arabidopsis circadian clock generates various rhythmic outputs that control various physiological events (Hotta et al, 2007; de Montaigu et al, 2010)

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