The C-terminal 17 amino acids of the photoreceptor UVR8 is involved in the fine-tuning of UV-B signaling^FA

Plant UV-B responses are mediated by the photoreceptor UV RESISTANCE LOCUS 8 (UVR8). In re-sponse to UV-B irradiation, UVR8 homodimers dissociate into monomers that bind to the E3 ubiquitin ligase CONSTITUTIVE PHOTOMORPHOGENIC1 (COP1). The in-teraction of the C27 domain in the C-terminal tail of UVR8 with the WD40 domain of COP1 is critical for UV-B sig-naling. However, the function of the last 17 amino acids (C17) of the C-terminus of UVR8, which are adjacent to C27, is unknown, although they are largely conserved in land plants. In this study, we established that Arabidopsis thaliana UVR8 C17 binds to full-length UVR8, but not to COP1, and reduces COP1 binding to the remaining portion of UVR8, including C27. We hypothesized that overexpression of C17 in a wild-type background would have a dominant negative effect on UVR8 activity;however, C17 overexpression caused strong silencing of endogenous UVR8, precluding a detailed analysis. We therefore generated YFP-UVR8N423 transgenic lines, in which C17 was deleted, to examine C17 function in-directly. YFP-UVR8N423 was more active than YFP-UVR8, suggesting that C17 inhibits UV-B signaling by attenuating binding between C27 and COP1. Our study reveals an inhibitory role for UVR8 C17 in fine-tuning UVR8–COP1 interactions during UV-B signaling.

Tomato SlRUP is a negative regulator of UV-B photomorphogenesis

Introduction Sunlight is an environmental factor regulating plant growth and development.Plants have evolved a battery of photoreceptors to sense and respond to different wavelengths of light(Jenkins,2017;Liu et al.,2020a).UV-B(280–315 nm)comprises the shortest wavelength of sunlight on the earth surface.In general,low fluence rate UV-B does not generate damage effects on plants,rather it induces plant photomorphogenic responses(Yin and Ulm,2017).High fluence rate UV-B may damage macromolecules,including nucleic acids,protein and membranes(Hideg et al.,2013).The UV-B photoreceptor UVR8 protein((UV RESISTANCE LOCUS 8)perceives the low dose UV-B and triggers UV-B specific signal transduction.