Plant photoreceptors and their signaling components compete for COP 1 binding via VP peptide motifs

Abstract

Plants sense different parts of the sun's light spectrum using distinct photoreceptors, which signal through the E3 ubiquitin ligase COP1. Here, we analyze why many COP1‐interacting transcription factors and photoreceptors harbor sequence‐divergent Val‐Pro (VP) motifs that bind COP1 with different 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 COP1. Photoactivation of UVR8 leads to high‐affinity cooperative binding of its VP motif and its photosensing core to COP1, preventing COP1 binding to its substrate HY5. UVR8–VP motif chimeras suggest that UV‐B signaling specificity resides in the UVR8 photoreceptor core. Different COP1–VP peptide motif complexes highlight sequence fingerprints required for COP1 targeting. The blue‐light photoreceptors CRY1 and CRY2 also compete with transcription factors for COP1 binding using similar VP motifs. Thus, our work reveals that different photoreceptors and their signaling components compete for COP1 via a conserved mechanism to control different light signaling cascades.

UVR8-mediated inhibition of shade avoidance involves HFR1 stabilization in Arabidopsis

“…In contrast to phytochrome and cryptochrome mechanisms involving direct protein-protein interactions with PIF4 and PIF5, no direct interaction has been detected between these transcription factors and UVR8 [28,32]. Moreover, whereas UVR8 is known to interact with and inhibit COP1 in response to UV-B [13,17,18], which is linked to PIF5 destabilization [32], our data suggest that PIF4 degradation under UV-B is independent of BOP2, despite clear stabilization of PIF4-HA in the bop2 background under our growth conditions that is in agreement with previously published data [48]. As PIF4 levels are also reduced in cop1-4 mutants and no additional UV-B-mediated degradation is detectable in the absence of functional COP1, COP1-mediated stabilization of PIF4 may be similarly disrupted by activated UVR8, as previously suggested for PIF5 [32].…”

“…The UVR8 photoreceptor contains a functionally relevant C-terminal domain with a domain that mimics the COP1 interaction domains of COP1 substrates, including that of HFR1 [18,45,58]. Activation of UVR8 results in high-affinity cooperative binding of COP1 through its VP motif and its photosensory domain, which prevents binding of COP1 to HFR1 and thus results in HFR1 stabilization under UV-B [18].…”

“…As HFR1 is a COP1 substrate and activated UVR8 inactivates COP1 [17,18,[42][43][44][45], we hypothesized that HFR1 stability is regulated by UVR8 in response to UV-B, which may contribute to the antagonistic effect of UV-B on SAS. We thus tested the effect of UV-B and low R:FR on HFR1 promoter-driven HFR1-HA protein levels in an uvr8 null mutant background compared to in a wild-type background.…”

“…COP1 is an E3 ubiquitin ligase that targets for proteasomal degradation transcriptional regulators that generally promote light responses and photomorphogenesis [15][16][17]. Interaction of activated UVR8 with COP1 leads to COP1 inactivation and thus accumulation of COP1 target proteins, such as the bZIP transcription factor ELONGATED HYPOCOTYL 5 (HY5) [13,18,19]. Stabilized HY5 is crucial for the regulation of numerous UV-B-induced genes, including those that function in UV-B acclimation and tolerance [14,[20][21][22][23][24][25][26].…”

LED light gradient as a screening tool for light quality responses in model plant species

“…Through this complex sensing machinery, light quality controls multiple plant developmental processes, such as germination, growth under competing canopies, root development, and flowering (6)(7)(8). Photoreceptors are integrative triggers ensuring a finetuned response to the whole light spectrum (9,10), while also interacting with hormonal pathways to coordinate plant growth and development (11,12). Moreover, there is an interplay between the signaling function of light, which is efficient even at very low irradiances, and its energetic function in photosynthesis, since some of the responses triggered by photoreceptors have a direct impact on photosynthesis efficiency (leaf inclination, leaf flattening, chloroplast movement), carbon metabolism, biomass production, and stress responses (13)(14)(15)(16)(17).…”