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Published on May 8, 2008; 10.1104/pp.108.121061

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Received April 11, 2008
Accepted April 24, 2008

AUXIN RESPONSES IN MUTANTS OF THE ARABIDOPSIS COP9 SIGNALOSOME

Esther Mirjam Natascha Dohmann , Mitchell Paul Levesque , Erika Isono , Markus Schmid , and Claus Schwechheimer *

Tubingen University, Center for Plant Molecular Biology, Department of Developmental Genetics, Auf der Morgenstelle 3-5, 72076 Tubingen, Germany; Max Planck Institute for Developmental Biology, Department of Genetics, Spemannstrasse 32, 72076 Tubingen, Germany; Max Planck Institute for Developmental Biology, Department of Molecular Biology, Spemannstrasse 32, 72076 Tubingen, Germany

* Corresponding author; email: claus.schwechheimer{at}zmbp.uni-tuebingen.de.

The 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, remained 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. While CSN had previously been shown to be required for the auxin response-regulatory E3 complexes, specifically SCFTIR1, the csn mutant phenotype suggests that CSN is not essential for auxin responses. We present physiological and genetic data, which 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.






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