title: Arabidopsis STO/BBX24 negatively regulates UV-B signaling by interacting with COP1 and repressing HY5 transcriptional activity.
abstract: UV-B (280-315 nm) is an integral part of solar radiation and can act either as a stress inducer or as a developmental signal. In recent years, increasing attention has been paid to the low-fluence UV-B-induced photomorphogenic response and several key players in this response have been identified, which include UVR8 (a UV-B-specific photoreceptor), COP1 (a WD40-repeat-containing RING finger protein), HY5 (a basic zipper transcription factor), and RUP1/2 (two UVR8-interacting proteins). Here we report that Arabidopsis SALT TOLERANCE (STO/BBX24), a known regulator for light signaling in plants, defines a new signaling component in UV-B-mediated photomorphogenesis. The bbx24 mutant is hypersensitive to UV-B radiation and becomes extremely dwarfed under UV-B treatment. By contrast, BBX24 overexpression transgenic lines respond much more weakly to UV-B than the bbx24 and wild-type plants. BBX24 expression is UV-B-inducible and its accumulation under UV-B requires COP1. Co-immunoprecipitation experiments indicate that BBX24 interacts with COP1 in planta upon UV-B illumination. Moreover, BBX24 interacts with HY5 and acts antagonistically with HY5 in UV-B-induced inhibition of hypocotyl elongation. Furthermore, BBX24 attenuates UV-B-induced HY5 accumulation and suppresses its transcription-activation activity. Taken together, our results reveal a previously uncharacterized function of the light-regulated BBX24 in UV-B responses and demonstrate that BBX24 functions as a negative regulator of photomorphogenic UV-B responses by interacting with both COP1 and HY5. The UV-B-inducible expression pattern and its suppression of HY5 activity suggest that BBX24 could be a new component of the feedback regulatory module of UV-B signaling in plants.
authors.affiliation: Key Laboratory of Ecology and Environmental Science in Guangdong Higher Education, School of Life Science, South China Normal University, Guangzhou, Guangdong 510631, China.
authors.forename: Lei
authors.initials: L
authors.lastname: Jiang
authors.forename: Yan
authors.initials: Y
authors.lastname: Wang
authors.forename: Qian-Feng
authors.initials: QF
authors.lastname: Li
authors.forename: Lars Olof
authors.initials: LO
authors.lastname: Björn
authors.forename: Jun-Xian
authors.initials: JX
authors.lastname: He
authors.forename: Shao-Shan
authors.initials: SS
authors.lastname: Li
mesh_terms: D017360:Arabidopsis / Q000254:growth & development / Q000378:metabolism* / Q000528:radiation effects; D029681:Arabidopsis Proteins / Q000378:metabolism*; D050976:Basic-Leucine Zipper Transcription Factors / Q000378:metabolism*; D018546:Hypocotyl / Q000378:metabolism; D047468:Immunoprecipitation; D009687:Nuclear Proteins / Q000378:metabolism*; D030821:Plants, Genetically Modified / Q000254:growth & development / Q000378:metabolism / Q000528:radiation effects; D025941:Protein Interaction Mapping; D015398:Signal Transduction; D015533:Transcriptional Activation; D044767:Ubiquitin-Protein Ligases / Q000378:metabolism*; D014466:Ultraviolet Rays
chemical_list: D029681:Arabidopsis Proteins; D050976:Basic-Leucine Zipper Transcription Factors; C109254:HY5 protein, Arabidopsis; D009687:Nuclear Proteins; C100336:STO protein, Arabidopsis; C471983:AT2G32950 protein, Arabidopsis; D044767:Ubiquitin-Protein Ligases