Formation of Nuclear Bodies of Arabidopsis CRY2 in Response to Blue Light Is Associated with Its Blue Light–Dependent Degradation

Abstract

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.

EIN3/EIL1 cooperate with PIF1 to prevent photo-oxidation and to promote greening of Arabidopsis seedlings

“…a cop-like phenotype in dark-grown seedlings (28,29). Interestingly, when 3-day-old CCT2 or 4-day-old CRY2-GFP etiolated seedlings were transferred to white light, we found that most of their cotyledons were unable to turn green ( Fig.…”

“…S1]. Conversely, a GFP-CRY2 overexpressing line that failed to show a cop-like phenotype (29) exhibited a normal cotyledon greening process (Fig. 1B and Fig.…”

Blue-light dependent ROS formation by Arabidopsis cryptochrome-2 may contribute toward its signaling role

“…1 There are 2 highly similar cryptochrome genes in Arabidopsis with overlapping functions but somewhat different light sensitivity; cry1 is stable at high light intensity whereas cry2 is rapidly degraded in the presence of blue light due to ubiquitination and targeting to the proteasome. 2 Until the present time, attempts to understand the mechanism of cry activation have focused on light-driven conformational change in the receptor that lead to interaction with transcription factors and/or elements of the proteasome. Certain changes in gene expression, for instance in the induction of flowering time and in de-etiolation responses have indeed been convincingly linked to cryptochrome interaction with these biological partners (reviewed in 1 ).…”

Insight into nuclear body formation of phytochromes through stochastic modelling and experiment

“…Fitting equation (18) to the experimentally measured number distribution we obtained an estimate for N s . Fitting equation (15) to the experimentally measured volume distribution we obtained estimates for δ, Δ, γ and the product K N s using ν = 0.64 and V 0 = 2.7× 10 −7 μm 3 . Using the estimate for N s we then obtained an estimate for K. For the maximum likelihood we used the fitdistr of the MASS package implemented in R [33].…”

“…Photoreceptors change conformation upon being activated by specific wavelengths of light and are subsequently transported to the nucleus where they form NBs, also sometimes referred to as spots or speckles. Notably, cryptochrome 2 (cry2) and two members of the phytochrome family, the light-labile phytochrome A (phyA) and light-stable phytochrome B (phyB), have been shown to form NBs when exposed to the required activating light conditions [10][11][12][13][14][15][16].…”