Cryptochrome-mediated blue-light signalling modulates UVR8 photoreceptor activity and contributes to UV-B tolerance in Arabidopsis

Nicolas Tissot,Roman Ulm

doi:10.1038/s41467-020-15133-y

Abstract

UV-B constitutes a critical part of the sunlight reaching the earth surface. The homodimeric plant UV-B photoreceptor UV RESISTANCE LOCUS 8 (UVR8) monomerizes in response to UV-B and induces photomorphogenic responses, including UV-B acclimation and tolerance. REPRESSOR OF UV-B PHOTOMORPHOGENESIS 1 (RUP1) and RUP2 are negative feedback regulators that operate by facilitating UVR8 ground state reversion through re-dimerization. Here we show that RUP1 and RUP2 are transcriptionally induced by cryptochrome photoreceptors in response to blue light, which is dependent on the bZIP transcriptional regulator ELONGATED HYPOCOTYL 5 (HY5). Elevated RUP1 and RUP2 levels under blue light enhance UVR8 re-dimerization, thereby negatively regulating UVR8 signalling and providing photoreceptor pathway cross-regulation in a polychromatic light environment, as is the case in nature. We further show that cryptochrome 1, as well as the red-light photoreceptor phytochrome B, contribute to UV-B tolerance redundantly with UVR8. Thus, photoreceptors for both visible light and UV-B regulate UV-B tolerance through an intricate interplay allowing the integration of diverse sunlight signals.

Highlights

UV-B constitutes a critical part of the sunlight reaching the earth surface
To test whether BIC1 and BIC2 overexpression modulates UV RESISTANCE LOCUS 8 (UVR8) activity, we UV-B treated various genotypes that were pre-treated with blue light or not, and quantified UVR8 re-dimerization after 30-min recovery
Cryptochromes form an equilibrium between active homodimeric and inactive monomeric states, whereas UVR8 equilibrates between an active monomeric and an inactive homodimeric state[6,17,34,35]

Summary

Introduction

UV-B constitutes a critical part of the sunlight reaching the earth surface. The homodimeric plant UV-B photoreceptor UV RESISTANCE LOCUS 8 (UVR8) monomerizes in response to UV-B and induces photomorphogenic responses, including UV-B acclimation and tolerance. We show that RUP1 and RUP2 are transcriptionally induced by cryptochrome photoreceptors in response to blue light, which is dependent on the bZIP transcriptional regulator ELONGATED HYPOCOTYL 5 (HY5). UVR8 monomers interact directly with the WD40 domain of the E3 ubiquitin ligase CONSTITUTIVELY PHOTOMORPHOGENIC 1 (COP1)[5,7]. The UVR8−COP1 interaction competes with that between COP1 and the photomorphogenesis-promoting bZIP transcription factor ELONGATED HYPOCOTYL 5 (HY5), thereby preventing its ubiquitination[8,9]. This leads to stabilization of HY5 and the induction of many target genes encoding proteins involved in the photomorphogenic response to UV-B, including HY5 itself[10,11,12]. It has been proposed that COP1 directly targets RUP1 and RUP2 for ubiquitination and degradation under UV-B, contributing to the stabilization of HY516

Methods

Results

Conclusion