Formation of nuclear bodies of Arabidopsis CRY2 in response to blue light is associated with its blue light-dependent degradation.
Arabidopsis thaliana cryptochrome 2 (CRY2) mediates photoperiodic promotion of floral initiation and blue light inhibition of hypocotyl elongation. It has been hypothesized that photoexcitation derepresses CRY2 by disengaging its C-terminal domain from the N-terminal PHR domain. To test this hypothesis, we analyzed activities of CRY2 fused to green fluorescent protein (GFP) at either the N terminus (GFP-CRY2) or the C terminus (CRY2-GFP). While GFP-CRY2 exerts light-dependent biochemical and physiological activities similar to those of the endogenous CRY2, CRY2-GFP showed constitutive biochemical and physiological activities. CRY2-GFP is constitutively phosphorylated, it promotes deetiolation in both dark and light, and it activates floral initiation in both long-day and short-day photoperiods. These results are consistent with the hypothesis that photoexcited CRY2 disengages its C-terminal domain from the PHR domain to become active. Surprisingly, we found that CRY2-GFP, but not GFP-CRY2, formed distinct nuclear bodies in response to blue light. Compared with GFP-CRY2 or the endogenous CRY2, CRY2-GFP degradation was significantly retarded in response to blue light, suggesting that the nuclear bodies may result from accumulation of photoexcited CRY2-GFP waiting to be degraded. Consistent with this interpretation, we showed that both GFP-CRY2 and endogenous CRY2 formed nuclear bodies in the presence of the 26S-proteasome inhibitors that block blue light-dependent CRY2 degradation.
Yu
Xuhong
X
Department of Molecular, Cell, and Developmental Biology, University of California, Los Angeles, California 90095, USA.
Sayegh
Ricardo
R
Maymon
Maskit
M
Warpeha
Katherine
K
Klejnot
John
J
Yang
Hongyun
H
Huang
Jie
J
Lee
Janet
J
Kaufman
Lon
L
Lin
Chentao
C
D017360:Arabidopsis / Q000166:cytology / Q000235:genetics / Q000378:metabolism* / Q000528:radiation effects; D029681:Arabidopsis Proteins / Q000235:genetics / Q000378:metabolism* / Q000528:radiation effects; D056931:Cryptochromes; D005420:Flavoproteins / Q000235:genetics / Q000378:metabolism* / Q000528:radiation effects; D018506:Gene Expression Regulation, Plant; D049452:Green Fluorescent Proteins / Q000235:genetics / Q000378:metabolism / Q000528:radiation effects; D045586:Intranuclear Inclusion Bodies / Q000378:metabolism*; D008027:Light; D008958:Models, Molecular; D010766:Phosphorylation; D055519:Photoreceptors, Plant / Q000378:metabolism; D046988:Proteasome Endopeptidase Complex / Q000378:metabolism; D018749:RNA, Plant / Q000235:genetics; D011993:Recombinant Fusion Proteins / Q000235:genetics / Q000378:metabolism / Q000528:radiation effects
D029681:Arabidopsis Proteins; C538962:CRY1 protein, Arabidopsis; C103618:CRY2 protein, Arabidopsis; D056931:Cryptochromes; D005420:Flavoproteins; D055519:Photoreceptors, Plant; D018749:RNA, Plant; D011993:Recombinant Fusion Proteins; D049452:Green Fluorescent Proteins; D046988:Proteasome Endopeptidase Complex; C061553:ATP dependent 26S protease