title: The RAD23 family provides an essential connection between the 26S proteasome and ubiquitylated proteins in Arabidopsis.
abstract: The ubiquitin (Ub)/26S proteasome system (UPS) directs the turnover of numerous regulatory proteins, thereby exerting control over many aspects of plant growth, development, and survival. The UPS is directed in part by a group of Ub-like/Ub-associated (UBL/UBA) proteins that help shuttle ubiquitylated proteins to the 26S proteasome for breakdown. Here, we describe the collection of UBL/UBA proteins in Arabidopsis thaliana, including four isoforms that comprise the RADIATION SENSITIVE23 (RAD23) family. The nuclear-enriched RAD23 proteins bind Ub conjugates, especially those linked internally through Lys-48, via their UBA domains, and associate with the 26S proteasome Ub receptor RPN10 via their N-terminal UBL domains. Whereas homozygous mutants individually affecting the four RAD23 genes are without phenotypic consequences (rad23a, rad23c, and rad23d) or induce mild phyllotaxy and sterility defects (rad23b), higher-order mutant combinations generate severely dwarfed plants, with the quadruple mutant displaying reproductive lethality. Both the synergistic effects of a rad23b-1 rpn10-1 combination and the response of rad23b plants to mitomycin C suggest that RAD23b regulates cell division. Taken together, RAD23 proteins appear to play an essential role in the cell cycle, morphology, and fertility of plants through their delivery of UPS substrates to the 26S proteasome.
authors.affiliation: Department of Genetics, University of Wisconsin, Madison, WI 53706, USA.
authors.forename: Lisa M
authors.initials: LM
authors.lastname: Farmer
authors.forename: Adam J
authors.initials: AJ
authors.lastname: Book
authors.forename: Kwang-Hee
authors.initials: KH
authors.lastname: Lee
authors.forename: Ya-Ling
authors.initials: YL
authors.lastname: Lin
authors.forename: Hongyong
authors.initials: H
authors.lastname: Fu
authors.forename: Richard D
authors.initials: RD
authors.lastname: Vierstra
mesh_terms: D000595:Amino Acid Sequence; D017360:Arabidopsis / Q000201:enzymology* / Q000235:genetics; D029681:Arabidopsis Proteins / Q000235:genetics / Q000378:metabolism*; D002455:Cell Division; D018744:DNA, Plant / Q000235:genetics; D004268:DNA-Binding Proteins / Q000235:genetics / Q000378:metabolism*; D020869:Gene Expression Profiling; D018507:Gene Expression Regulation, Developmental; D018506:Gene Expression Regulation, Plant; D008969:Molecular Sequence Data; D009154:Mutation; D010802:Phylogeny; D046988:Proteasome Endopeptidase Complex / Q000235:genetics / Q000378:metabolism*; D020033:Protein Isoforms / Q000235:genetics / Q000378:metabolism; D020543:Proteome / Q000378:metabolism; D016415:Sequence Alignment; D025801:Ubiquitin / Q000235:genetics / Q000378:metabolism*; D054875:Ubiquitination
chemical_list: D029681:Arabidopsis Proteins; D018744:DNA, Plant; D004268:DNA-Binding Proteins; D020033:Protein Isoforms; D020543:Proteome; C583232:RAD23a protein, Arabidopsis; D025801:Ubiquitin; D046988:Proteasome Endopeptidase Complex; C061553:ATP dependent 26S protease