title: Auxin responses in mutants of the Arabidopsis CONSTITUTIVE PHOTOMORPHOGENIC9 signalosome.
abstract: The CONSTITUTIVE PHOTOMORPHOGENIC9 (COP9) signalosome (CSN) is an evolutionarily conserved multiprotein complex that interacts with cullin-RING type E3 ubiquitin ligases (CRLs). CSN subunit 5 (CSN5), which, when incorporated into CSN, can deconjugate the NEDD8 modification from the cullin subunit of CRLs, is essential for CSN's role in controlling CRL activity. Whether the CSN5 monomer, which is maintained in csn mutants such as csn3 or csn4, has a functional role, remains to be established. We performed a comparative gene expression-profiling experiment with Arabidopsis (Arabidopsis thaliana) csn3, csn4, and csn5 mutants, and we show here that these mutants cannot be distinguished at the transcriptional level. Furthermore, we show that csn3 csn5 mutants are morphologically indistinguishable from csn3 or csn5 mutants. Taken together, these data suggest that the CSN5 monomer does not have a function that leads to transcriptional or morphological changes in the csn mutants. We further examined auxin responses in csn mutants. Whereas CSN had previously been shown to be required for the auxin response-regulatory E3 complexes, specifically SCF(TIR1), the csn mutant phenotype suggests that CSN is not essential for auxin responses. We present physiological and genetic data that indicate that auxin responses are indeed only partially impaired in csn mutants and that this is not the result of maternally contributed CSN. Finally, we discuss these findings in the context of the current understanding of the role of neddylation and CSN-mediated deneddylation for CRL activity.
authors.affiliation: Department of Developmental Genetics, Center for Plant Molecular Biology, Tübingen University, 72076 Tuebingen, Germany.
authors.forename: Esther Mirjam Natascha
authors.initials: EM
authors.lastname: Dohmann
authors.forename: Mitchell Paul
authors.initials: MP
authors.lastname: Levesque
authors.forename: Erika
authors.initials: E
authors.lastname: Isono
authors.forename: Markus
authors.initials: M
authors.lastname: Schmid
authors.forename: Claus
authors.initials: C
authors.lastname: Schwechheimer
mesh_terms: D017360:Arabidopsis / Q000235:genetics / Q000254:growth & development / Q000378:metabolism*; D029681:Arabidopsis Proteins / Q000235:genetics / Q000378:metabolism*; D000075686:COP9 Signalosome Complex; D044842:Cullin Proteins / Q000378:metabolism*; D020869:Gene Expression Profiling; D018506:Gene Expression Regulation, Plant; D007210:Indoleacetic Acids / Q000378:metabolism*; D009154:Mutation; D009687:Nuclear Proteins / Q000235:genetics / Q000378:metabolism*; D020411:Oligonucleotide Array Sequence Analysis; D010641:Phenotype; D011494:Protein Kinases / Q000235:genetics / Q000378:metabolism*
chemical_list: D029681:Arabidopsis Proteins; C497728:COP9 signalosome subunit 5, Arabidopsis; D044842:Cullin Proteins; C000618792:FUS11 protein, Arabidopsis; D007210:Indoleacetic Acids; D009687:Nuclear Proteins; D011494:Protein Kinases; D000075686:COP9 Signalosome Complex