title: The E2 ubiquitin-conjugating enzymes, AtUBC1 and AtUBC2, play redundant roles and are involved in activation of FLC expression and repression of flowering in Arabidopsis thaliana.
abstract: Post-translational modifications of proteins by addition of ubiquitin can regulate protein degradation and localization, protein-protein interactions and transcriptional activation. In the ubiquitylation system, substrate specificity is primarily determined by the E2 ubiquitin-conjugating enzyme (UBC) and the E3 ubiquitin ligase. The Arabidopsis thaliana genome contains 37 genes encoding UBC homologs. However, the biological functions of these genes remain largely uncharacterized. Here, we report reverse genetic characterization of AtUBC1 and AtUBC2. While the loss-of-function single mutants Atubc1-1 and Atubc2-1 only show weak phenotypes, the double mutant Atubc1-1 Atubc2-1 shows a dramatically reduced number of rosette leaves and an early-flowering phenotype. Consistent with these results, the transcript levels of the floral repressor genes FLOWERING LOCUS C (FLC), MADS ASSOCIATED FLOWERING 4 (MAF4) and MAF5 are reduced in the double mutant. Loss-of-function mutants of HISTONE MONOUBIQUITINATION 1 (HUB1) and HUB2, which were previously reported to encode an E3 involved in histone H2B ubiquitylation, also show an early-flowering phenotype and reduced levels of FLC, MAF4 and MAF5 transcripts. In both Atubc1-1 Atubc2-1 and hub2-2 mutants, H2B mono-ubiquitylation is drastically reduced. Taken together, our results indicate that E2s AtUBC1/AtUBC2 and E3s HUB1/HUB2 together mediate H2B ubiquitylation, which is involved in the activation of floral repressor genes as well as in other processes as indicated by the pleiotropic phenotypes of the mutants.
authors.affiliation: Institut de Biologie Moléculaire des Plantes (IBMP), Laboratoire Propre du CNRS (UPR2357) conventionné avec l'Université Louis Pasteur Strasbourg 1, 12 rue du Général Zimmer, 67084 Strasbourg Cedex, France.
authors.forename: Lin
authors.initials: L
authors.lastname: Xu
authors.forename: Rozenn
authors.initials: R
authors.lastname: Ménard
authors.forename: Alexandre
authors.initials: A
authors.lastname: Berr
authors.forename: Jörg
authors.initials: J
authors.lastname: Fuchs
authors.forename: Valérie
authors.initials: V
authors.lastname: Cognat
authors.forename: Denise
authors.initials: D
authors.lastname: Meyer
authors.forename: Wen-Hui
authors.initials: WH
authors.lastname: Shen
mesh_terms: D017360:Arabidopsis / Q000201:enzymology* / Q000235:genetics; D029681:Arabidopsis Proteins / Q000235:genetics / Q000378:metabolism*; D004269:DNA, Bacterial / Q000235:genetics; D035264:Flowers / Q000201:enzymology / Q000235:genetics*; D018506:Gene Expression Regulation, Plant; D017343:Genes, Plant; D005816:Genetic Complementation Test; D006657:Histones / Q000378:metabolism; D026161:MADS Domain Proteins / Q000378:metabolism*; D016254:Mutagenesis, Insertional; D010641:Phenotype; D018515:Plant Leaves / Q000201:enzymology / Q000235:genetics; D018749:RNA, Plant / Q000235:genetics; D044763:Ubiquitin-Conjugating Enzymes / Q000235:genetics / Q000378:metabolism*; D044767:Ubiquitin-Protein Ligases / Q000378:metabolism; D054875:Ubiquitination
chemical_list: D029681:Arabidopsis Proteins; D004269:DNA, Bacterial; C418902:At5g10140 protein, Arabidopsis; D006657:Histones; D026161:MADS Domain Proteins; D018749:RNA, Plant; C036483:T-DNA; C489357:UBC1 protein, Arabidopsis; D044763:Ubiquitin-Conjugating Enzymes; C521255:HUB1 protein, Arabidopsis; C521256:HUB2 protein, Arabidopsis; D044767:Ubiquitin-Protein Ligases