UV-B Promotes Rapid Nuclear Translocation of the Arabidopsis UV-B–Specific Signaling Component UVR8 and Activates Its Function in the Nucleus

Abstract

Arabidopsis thaliana UV RESISTANCE LOCUS8 (UVR8) is a UV-B-specific signaling component that binds to chromatin and regulates UV protection by orchestrating expression of a range of genes. Here, we studied how UV-B regulates UVR8. We show that UV-B stimulates the nuclear accumulation of both a green fluorescent protein (GFP)-UVR8 fusion and native UVR8. Nuclear accumulation leads to UV-B induction of the HY5 gene, encoding a key transcriptional effector of the UVR8 pathway. Nuclear accumulation of UVR8 is specific to UV-B, occurs at low fluence rates, and is observed within 5 min of UV-B exposure. Attachment of a nuclear export signal (NES) to GFP-UVR8 causes cytosolic localization in the absence of UV-B. However, UV-B promotes rapid nuclear accumulation of NES-GFP-UVR8, indicating a concerted mechanism for nuclear translocation. UVR8 lacking the N-terminal 23 amino acids is impaired in nuclear translocation. Attachment of a nuclear localization signal (NLS) to UVR8 causes constitutive nuclear localization. However, NLS-GFP-UVR8 only confers HY5 gene expression following UV-B illumination, indicating that nuclear localization, although necessary for UVR8 function, is insufficient to cause expression of target genes; UV-B is additionally required to stimulate UVR8 function in the nucleus. These findings provide new insights into the mechanisms through which UV-B regulates gene expression in plants.

Retracted: Nitric oxide enhances plant ultraviolet‐B protection up‐regulating gene expression of the phenylpropanoid biosynthetic pathway

“…UV-B supports the rapid nuclear accumulation of UVR8 that activates the expression of the basic leucine-zipper transcription factor ELONGATED HYPOCOTYL5 (HY5). It was shown that the increased transcription of HY5 confers UV protection (Kaiserli & Jenkins 2007;Jenkins 2009). It was recently reported that MYB12, the Arabidopsis functional homolog of ZmP is one of the target genes of HY5 (Stracke et al 2010).…”

Impact of UV-B on drought- or cadmium-induced changes in the fatty acid composition of membrane lipid fractions in wheat

“…The synthesis of flavonoids is stimulated by very low doses of UV-B within a few hours, although this response is not specific to UV-B exposure, and there are considerable differences both between species and between the levels of flavonoid compounds regulated by UV-B (Jenkins, 2008). Mutant plant genotypes with impaired flavonoid biosynthesis are more susceptible to damage by UV-B (Kaiserli and Jenkins, 2007). Interestingly, in Arabidopsis it was found that the roots, rather than other organs, perceive the UV-B signal (Tong et al, 2008).…”

Reversion of the Arabidopsis UV-B photoreceptor UVR8 to the homodimeric ground state

“…Rabbit polyclonal antibodies were generated against synthetic peptides derived from the UVR8 protein sequence [amino acids 410-424 + C: VPDETGLTDGSSKGNC; anti-UVR8 (410-424) ] and the COP1 protein sequence [amino acids C + 13-26: CVKPDPRTSSVGEGA; anti-COP1 (13)(14)(15)(16)(17)(18)(19)(20)(21)(22)(23)(24)(25)(26) ] and were affinity-purified against the peptide (Eurogentec). Guinea pig polyclonal antibodies were generated against a synthetic peptide [amino acids C + 426-440: CGDISVPQTDVKRVRI; anti-UVR8 (426-440) ] already previously used to generate polyclonal UVR8 antibodies in rabbits (4) and were affinity-purified against the peptide (Eurogentec).…”

“…Upon UV-B exposure, the RUP1 and RUP2 genes are transcriptionally activated in a UVR8-dependent manner. RUP1-and RUP2-YFP fusion proteins localize to both the nucleus and the cytoplasm (22), mimicking the subcellular localization of UVR8 (23). RUP1 and RUP2 are known to repress the UV-B-signaling pathway, but the mechanism by which they do so is presently unknown (22).…”