title: SHORT HYPOCOTYL UNDER BLUE1 truncations and mutations alter its association with a signaling protein complex in Arabidopsis.
abstract: Higher plants monitor their ambient light signals through red/far-red absorbing phytochromes and blue/UV-A light absorbing cryptochromes. Subsequent signaling cascades alter gene expression and initiate morphogenic responses. We previously isolated SHORT HYPOCOTYL UNDER BLUE1 (SHB1), a putative transcriptional coactivator in light signaling. SHB1 is homologous to the SYG1 protein family and contains an N-terminal SPX domain and a C-terminal EXS domain. Overaccumulation of the SPX domain caused a long hypocotyl phenotype similar to that of shb1-D under red, far-red, or blue light. By contrast, overaccumulation of the C-terminal EXS domain led to a short hypocotyl phenotype similar to that of shb1 under blue light. The N-terminal SPX domain was associated with a smaller protein complex than the native protein complex associated with endogenous SHB1. By contrast, the EXS domain was associated with a slightly smaller protein complex than the native protein complex, but it largely displaced endogenous SHB1 from its native protein complex. In addition, all six missense mutations that we identified from a suppressor screen were clustered within or close to the SPX domain, and these mutations impaired the assembly of the SHB1-containing protein complex. We propose that both SPX and EXS domains likely anchor SHB1 to a protein complex, and the SPX domain is critical for SHB1 signaling.
authors.affiliation: Department of Plant Biology, University of Minesota, St. Paul, Minesota 55108, USA.
authors.forename: Yun
authors.initials: Y
authors.lastname: Zhou
authors.forename: Min
authors.initials: M
authors.lastname: Ni
mesh_terms: D017360:Arabidopsis / Q000235:genetics* / Q000378:metabolism; D029681:Arabidopsis Proteins / Q000235:genetics / Q000378:metabolism*; D018506:Gene Expression Regulation, Plant; D018546:Hypocotyl / Q000254:growth & development; D046912:Multiprotein Complexes / Q000378:metabolism*; D016297:Mutagenesis, Site-Directed; D020125:Mutation, Missense; D010641:Phenotype; D030821:Plants, Genetically Modified / Q000235:genetics / Q000378:metabolism; D054730:Protein Interaction Domains and Motifs
chemical_list: D029681:Arabidopsis Proteins; D046912:Multiprotein Complexes; C511745:SHB1 protein, Arabidopsis