Functional analysis of a 450-amino acid N-terminal fragment of phytochrome B in Arabidopsis.
Phytochrome, a major photoreceptor in plants, consists of two domains: the N-terminal photosensory domain and the C-terminal domain. Recently, the 651-amino acid photosensory domain of phytochrome B (phyB) has been shown to act as a functional photoreceptor in the nucleus. The phytochrome (PHY) domain, which is located at the C-terminal end of the photosensory domain, is required for the spectral integrity of phytochrome; however, little is known about the signal transduction activity of this domain. Here, we have established transgenic Arabidopsis thaliana lines expressing an N-terminal 450-amino acid fragment of phyB (N450) lacking the PHY domain on a phyB-deficient background. Analysis of these plants revealed that N450 can act as an active photoreceptor when attached to a short nuclear localization signal and beta-glucuronidase. In vitro spectral analysis of reconstituted chromopeptides further indicated that the stability of the N450 Pfr form, an active form of phytochrome, is markedly reduced in comparison with the Pfr form of full-length phyB. Consistent with this, plants expressing N450 failed to respond to intermittent light applied at long intervals, indicating that N450 Pfr is short-lived in vivo. Taken together, our findings show that the PHY domain is dispensable for phyB signal transduction but is required for stabilizing the Pfr form of phyB.
Laboratory of Plant Physiology, Graduate School of Science, Kyoto University, Kitashirakawa-Oiwake-Cho, Sakyo-Ku, Kyoto 606-8502, Japan.
Yoshito
Y
Oka
Tomonao
T
Matsushita
Nobuyoshi
N
Mochizuki
Tomomi
T
Suzuki
Satoru
S
Tokutomi
Akira
A
Nagatani
D017360:Arabidopsis / Q000033:anatomy & histology / Q000235:genetics / Q000378:metabolism*; D029681:Arabidopsis Proteins / Q000235:genetics / Q000378:metabolism*; D002467:Cell Nucleus / Q000378:metabolism; D008027:Light; D008969:Molecular Sequence Data; D009154:Mutation; D010446:Peptide Fragments / Q000235:genetics / Q000378:metabolism*; D010786:Photoreceptor Cells / Q000378:metabolism*; D010834:Phytochrome / Q000235:genetics / Q000378:metabolism*; D051939:Phytochrome B; D030821:Plants, Genetically Modified; D017434:Protein Structure, Tertiary; D011993:Recombinant Fusion Proteins / Q000235:genetics / Q000378:metabolism; D015398:Signal Transduction / Q000502:physiology; D014157:Transcription Factors / Q000235:genetics / Q000378:metabolism*
D029681:Arabidopsis Proteins; C497952:PHYB protein, Arabidopsis; D010446:Peptide Fragments; D011993:Recombinant Fusion Proteins; D014157:Transcription Factors; D010834:Phytochrome; D051939:Phytochrome B