Journal Article

Functional Analysis of Amino-Terminal Domains of the Photoreceptor Phytochrome B

Nagy, Ferenc, Ádám, Éva, Mérai, Zsuzsanna, Terecskei, Kata, Schäfer, Eberhard, Kevei, Éva, Palágyi, Andrea, Kircher, Stefan, Kozma-Bognár, László

2010

Overview

At the core of the circadian network in Arabidopsis (Arabidopsis thaliana), clock genes/proteins form multiple transcriptional/translational negative feedback loops and generate a basic approximately 24-h oscillation, which provides daily regulation for a wide range of processes. This temporal organization enhances the fitness of plants only if it corresponds to the natural day/night cycles. Light, absorbed by photoreceptors, is the most effective signal in synchronizing the oscillator to environmental cycles. Phytochrome B (PHYB) is the major red/far-red light-absorbing phytochrome receptor in light-grown plants. Besides modulating the pace and phase of the circadian clock, PHYB controls photomorphogenesis and delays flowering. It has been demonstrated that the nuclear-localized amino-terminal domain of PHYB is capable of controlling photomorphogenesis and, partly, flowering. Here, we show (1) that PHYB derivatives containing 651 or 450 amino acid residues of the amino-terminal domains are functional in mediating red light signaling to the clock, (2) that circadian entrainment is a nuclear function of PHYB, and (3) that a 410-amino acid amino-terminal fragment does not possess any functions of PHYB due to impaired chromophore binding. However, we provide evidence that the carboxyl-terminal domain is required to mediate entrainment in white light, suggesting a role for this domain in integrating red and blue light signaling to the clock. Moreover, careful analysis of the circadian phenotype of phyB-9 indicates that PHYB provides light signaling for different regulatory loops of the circadian oscillator in a different manner, which results in an apparent decoupling of the loops in the absence of PHYB under specific light conditions.

• Publisher: American Society of Plant Biologists
• Subject: amino acids / Arabidopsis / Arabidopsis - chemistry / Arabidopsis - genetics / Arabidopsis - radiation effects / Arabidopsis Proteins / Arabidopsis Proteins - chemistry / Arabidopsis thaliana / Biological and medical sciences / chemistry / Circadian Rhythm / Flowering / Fluence / Fundamental and applied biological sciences. Psychology / Gene Expression Regulation, Plant / genes / Genetic Complementation Test / genetics / Hypocotyls / Light / Oscillators / Phenotypes / photomorphogenesis / Photoreceptors / phytochrome / Phytochrome B / Phytochrome B - chemistry / Plant cells / Plant physiology and development / Plants / Plants, Genetically Modified / Plants, Genetically Modified - chemistry / Plants, Genetically Modified - genetics / Proteins / radiation effects / Recombinant Fusion Proteins / Recombinant Fusion Proteins - chemistry / red light / RNA, Plant / RNA, Plant - genetics / Seedlings / SYSTEMS BIOLOGY, MOLECULAR BIOLOGY, AND GENE REGULATION / white light