Photoreceptor signaling: when COP1 meets VPs

Abstract

How structurally distinct photoreceptors regulate evolutionarily diverse transcription factors to modulate common photoresponses is an intriguing question in plant biology. In this issue of The EMBO Journal, Lau et al demonstrate that COP1, the substrate receptor of E3 ubiquitin ligase CUL4COP1‐SPAs, interacts with the diverse VP motif‐containing transcription factors and photoreceptors via its highly plastic WD40 domain. Light‐activated photoreceptors increase their affinity to COP1 to outcompete the COP1‐interacting transcription factors, allowing their accumulation and inducing photomorphogenic development of plants.

The Photomorphogenic Central Repressor COP1: Conservation and Functional Diversification during Evolution

“…COP1 interacts with both photoreceptors and its target transcription factors via its WD40 repeats. The components of such photoreceptor–COP1–target modules seem to have co-evolved to preserve their tripartite interaction pattern during plant terrestrialization ( Lau et al., 2019 , Wang and Lin, 2019 ).…”

“…COP1 is a highly conserved E3 ligase that possibly originated in the common ancestor of all eukaryotes. COP1 is involved in diverse biological processes in plants and animals, including development and metabolism, and responses to abiotic and biotic stimuli ( Lau and Deng, 2012 , Marine, 2012 , Artz et al., 2019 , Sharma et al., 2019 , Tokutsu et al., 2019 , Wang and Lin, 2019 ). The pleiotropic roles of COP1 are at least partly determined by its functional domains, which are responsible for flexible protein–protein interactions ( Uljon et al., 2016 ).…”

Allelic variation of BBX24 is a dominant determinant controlling red coloration and dwarfism in pear

“…When the cells are in darkness, COP1 is localized in the nuclei, and the light receptors UVR8, CRYs, and PHYs are inactive; the COP1/SPAs complex interacts with the VP motif of the substrate these COP1‐target factors to facilitate their degradation via the 26S proteasome. When the cells are exposed to the light, COP1 will transfer to the cytoplasm, and the light receptors, including UVR8 and CRYs, could interact with COP1 to outcompete and suppress its activity, resulting in their stabilization (Wang and Lin, 2019; Yan et al ., 2011). Given that PyBBX24 was exclusively located in nuclei, and PyBBX24 ΔN14 were detected in both nuclei and cytoplasm in N. benthamiana leaves (Figure S17), we hypothesize that PyBBX24 perhaps undergoes COP1‐mediated ubiquitination in darkness, resulting in the instability of PyBBX24.…”

Constitutive Photomorphogenic 1 Enhances ER Stress Tolerance in Arabidopsis

“…In the dark condition, COP1 suppresses photomorphogenesis by translocating from the cytosol to the nucleus, which in turn results in the degradation of HY5 [ 5 , 8 ]. In this study, HY5 was partially degraded by COP1 under the ER stress condition ( Figure 3 ), suggesting that COP1 mediates ER stress response through HY5 [ 38 ].…”

“…On the other hand, in the absence of light, COP1 mediates the ubiquitination and degradation of HY5 [ 6 , 7 ]. Interestingly, photoreceptors are also the targets of COP1 [ 8 ], while PHYs mediate the nuclear exclusion of COP1, thus repressing its activity [ 9 ]. Therefore, in the light signaling pathway, COP1 acts as a central negative regulator and as an E3 ligase, and its nuclear exclusion is a rate-limiting step.…”