Functional analysis of amino-terminal domains of the photoreceptor phytochrome B.
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.
Palágyi
Andrea
A
Institute of Plant Biology, Biological Research Centre of the Hungarian Academy of Sciences, H-6726 Szeged, Hungary.
Terecskei
Kata
K
Adám
Eva
E
Kevei
Eva
E
Kircher
Stefan
S
Mérai
Zsuzsanna
Z
Schäfer
Eberhard
E
Nagy
Ferenc
F
Kozma-Bognár
László
L
D017360:Arabidopsis / Q000737:chemistry* / Q000235:genetics / Q000528:radiation effects; D029681:Arabidopsis Proteins / Q000737:chemistry*; D002940:Circadian Rhythm; D018506:Gene Expression Regulation, Plant; D005816:Genetic Complementation Test; D008027:Light; D051939:Phytochrome B / Q000737:chemistry*; D030821:Plants, Genetically Modified / Q000737:chemistry / Q000235:genetics; D018749:RNA, Plant / Q000235:genetics; D011993:Recombinant Fusion Proteins / Q000737:chemistry
D029681:Arabidopsis Proteins; C497952:PHYB protein, Arabidopsis; D018749:RNA, Plant; D011993:Recombinant Fusion Proteins; D051939:Phytochrome B