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.
Institute of Plant Biology, Biological Research Centre of the Hungarian Academy of Sciences, H-6726 Szeged, Hungary.
Andrea
A
Palágyi
Kata
K
Terecskei
Eva
E
Adám
Eva
E
Kevei
Stefan
S
Kircher
Zsuzsanna
Z
Mérai
Eberhard
E
Schäfer
Ferenc
F
Nagy
László
L
Kozma-Bognár
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