1.
Two distinct domains of the UVR8 photoreceptor interact with COP1 to initiate UV-B signaling in Arabidopsis.
Abstract:
UV-B photon reception by the Arabidopsis thaliana homodimeric UV RESISTANCE LOCUS8 (UVR8) photoreceptor leads to its monomerization and a crucial interaction with CONSTITUTIVELY PHOTOMORPHOGENIC1 (COP1). Relay of the subsequent signal regulates UV-B-induced photomorphogenesis and stress acclimation. Here, we report that two separate domains of UVR8 interact with COP1: the β-propeller domain of UVR8 mediates UV-B-dependent interaction with the WD40 repeats-based predicted β-propeller domain of COP1, whereas COP1 activity is regulated by interaction through the UVR8 C-terminal C27 domain. We show not only that the C27 domain is required for UVR8 activity but also that chemically induced expression of the C27 domain is sufficient to mimic UV-B signaling. We further show, in contrast with COP1, that the WD40 repeat proteins REPRESSOR OF UV-B PHOTOMORPHOGENESIS1 (RUP1) and RUP2 interact only with the UVR8 C27 domain. This coincides with their facilitation of UVR8 reversion to the ground state by redimerization and their potential to interact with UVR8 in a UV-B-independent manner. Collectively, our results provide insight into a key mechanism of photoreceptor-mediated signaling and its negative feedback regulation.
2.
The UVR8 UV-B Photoreceptor: Perception, Signaling and Response.
Abstract:
Ultraviolet-B radiation (UV-B) is an intrinsic part of sunlight that is accompanied by significant biological effects. Plants are able to perceive UV-B using the UV-B photoreceptor UVR8 which is linked to a specific molecular signaling pathway and leads to UV-B acclimation. Herein we review the biological process in plants from initial UV-B perception and signal transduction through to the known UV-B responses that promote survival in sunlight. The UVR8 UV-B photoreceptor exists as a homodimer that instantly monomerises upon UV-B absorption via specific intrinsic tryptophans which act as UV-B chromophores. The UVR8 monomer interacts with COP1, an E3 ubiquitin ligase, initiating a molecular signaling pathway that leads to gene expression changes. This signaling output leads to UVR8-dependent responses including UV-B-induced photomorphogenesis and the accumulation of UV-B-absorbing flavonols. Negative feedback regulation of the pathway is provided by the WD40-repeat proteins RUP1 and RUP2, which facilitate UVR8 redimerization, disrupting the UVR8-COP1 interaction. Despite rapid advancements in the field of recent years, further components of UVR8 UV-B signaling are constantly emerging, and the precise interplay of these and the established players UVR8, COP1, RUP1, RUP2 and HY5 needs to be defined. UVR8 UV-B signaling represents our further understanding of how plants are able to sense their light environment and adjust their growth accordingly.
