The central circadian clock proteins CCA1 and LHY regulate iron homeostasis in Arabidopsis

Circadian clock is the endogenous time-keeping machinery that synchronizes an organism's metabolism, behavior, and physiology to the daily light-dark circles, thereby contributing to organismal fitness. Iron (Fe) is an essential micronutrient for all organisms and it plays important roles in diverse processes of plant growth and development. Here, we show that, in Arabidopsis thaliana, loss of the central clock genes, CIRCADIAN CLOCK ASSOCIATED 1 (CCA1) and LATE ELONGATED HYPOCOTYL (LHY), results in both reduced Fe uptake and photosynthetic efficiency, whereas CCA1 overexpression confers the opposite effects. We show that root Fe(III) reduction activity, and expression of FERRIC REDUCTION OXIDASE 2 (FRO2) and IRON-REGULATED TRANSPORTER 1 (IRT1) exhibit circadian oscillations, which are disrupted in the cca1 lhy double mutant. Furthermore, CCA1 directly binds to the specific regulatory regions of multiple Fe homeostasis genes and activates their expression. Thus, this study established that, in plants, CCA1 and LHY function as master regulators that maintain cyclic Fe homeostasis.