Plant photoreceptors and their signaling components compete for binding to the ubiquitin ligase COP1 using their VP-peptide motifs

Abstract

Plants sense different parts of the sun's light spectrum using specialized photoreceptors, many of which signal through the E3 ubiquitin ligase COP1. Photoreceptor binding modulates COP1's ubiquitin ligase activity towards transcription factors. Here we analyze why many COP1-interacting transcription factors and photoreceptors harbor sequence-divergent Val-Pro (VP) peptide motifs. We demonstrate that VP motifs enable different light signaling components to bind to the WD40 domain of COP1 with various binding affinities. Crystal structures of the VP motifs of the UV-B photoreceptor UVR8 and the transcription factor HY5 in complex with COP1, quantitative binding assays and reverse genetic experiments together suggest that UVR8 and HY5 compete for the COP1 WD40 domain. Photoactivation of UVR8 leads to high-affinity cooperative binding of its VP domain and its photosensing core to COP1, interfering with the binding of COP1 to its substrate HY5. Functional UVR8 -VP motif chimeras suggest that UV-B signaling specificity resides in the UVR8 photoreceptor core, not its VP motif. Crystal structures of different COP1 -VP peptide complexes highlight sequence fingerprints required for COP1 targeting. The functionally distinct blue light receptors CRY1 and CRY2 also compete with downstream transcription factors for COP1 binding using similar VP-peptide motifs. Together, our work reveals that photoreceptors and

Degradation of the transcription factors PIF4 and PIF5 under UV‐B promotes UVR8‐mediated inhibition of hypocotyl growth in Arabidopsis

“…A BLADE‐ON‐PETIOLE 1 (BOP1)‐ and BOP2‐based E3 ubiquitin ligase complex has been shown to ubiqitinate PIF4, thereby affecting photo‐ and thermomorphogenesis (Zhang et al , ); however, involvement of this complex in degradation of PIF4 under UV‐B remains to be demonstrated. Activity of COP1, on the other hand, is a direct target of UVR8 (Favory et al , ; Podolec and Ulm, ; Lau et al , ), and COP1 has been shown to facilitate the stability of PIF family proteins, including PIF4 and PIF5, in the dark (Bauer et al , ; Gangappa and Kumar, ; Pham et al , ). This UVR8‐mediated inhibition of COP1 may thus be linked to degradation of PIF4 and PIF5, although via a currently unknown mechanism.…”

The photoreceptor UVR8 mediates the perception of both UV-B and UV-A wavelengths up to 350 nm of sunlight with responsivity moderated by cryptochromes

“…indicating that the crosstalk between UV-B/UV-A sw and UV-A lw /blue signaling pathways may 561 involve RUPs. In addition, a recent study demonstrated that both UVR8 and CRYs use VP motifs to 562 compete for binding the WD40 domain of COP1 (Lau et al, 2019). Therefore, crosstalk between 563 the two signaling pathways could involve COP1.…”

Photoreceptor signaling: when COP1 meets VPs

“…However, the exact structural mechanisms underlying this photoreceptor–COP1–substrate tripartite interaction and how the evolutionarily distinct photoreceptors converge on the single hub protein COP1 remained unclear. In this issue of The EMBO Journal , a study from the Roman Ulm and Michael Hothorn's groups at University of Geneva solved, at least partially, these structure‐function problems (Lau et al , ).…”

“…An earlier study showed that three COP1‐interacting proteins bear a common sequence motif, referred to as VP, which contains two amino acids, valine–proline, as the invariable core, and that the VP motif may be a common COP1‐binding site (Holm et al , ). Lau et al () showed that six transcription factors (HY5, HYH, CO, COL3, STO, and HFR1) and three photoreceptors (CRY1, CRY2, and UVR8) all possess the VP motifs. They examined the crystal structures of the complexes of the WD40 domain of COP1 (326 residues) and individual VP motifs (< 10 residues) of those nine COP1‐interacting proteins, demonstrating that the core residues of the VP motifs form the center of the COP1‐binding site, whereas the chemically diverse residues at the −3 and −2 position of the VP motifs act as anchor residues by inserting deeply into the VP‐binding cleft of COP1.…”