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The RUB/Nedd8 conjugation pathway is required for early development in Arabidopsis

Sunethra Dharmasiri, Nihal Dharmasiri, Hanjo Hellmann, Mark Estelle

Author Affiliations

  1. Sunethra Dharmasiri1,
  2. Nihal Dharmasiri1,
  3. Hanjo Hellmann2 and
  4. Mark Estelle*,1
  1. 1 Department of Biology and Indiana Molecular Biology Institute, Indiana University, Bloomington, IN, 47405, Germany
  2. 2 Institut für Angewandte Genetik, Molekulare Entwicklungsbiologie der Pflanzen, Albrecht‐Thaer Weg 6, D‐14195, Berlin, Germany
  1. *Corresponding author. E-mail: mestelle{at}bio.indiana.edu
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Abstract

The related‐to‐ubiquitin (RUB) protein is post‐translationally conjugated to the cullin subunit of the SCF (SKP1, Cullin, F‐box) class of ubiquitin protein ligases. Although the precise biochemical function of RUB modification is unclear, studies indicate that the modification is important for SCF function. In Arabidopsis, RUB modification of CUL1 is required for normal function of SCFTIR1, an E3 required for response to the plant hormone auxin. In this report we show that an Arabidopsis protein called RCE1 functions as a RUB‐conjugating enzyme in vivo. A mutation in the RCE1 gene results in a phenotype like that of the axr1 mutant. Most strikingly, plants deficient in both RCE1 and AXR1 have an embryonic phenotype similar to mp and bdl mutants, previously shown to be deficient in auxin signaling. Based on these results, we suggest that the RUB‐conjugation pathway is required for auxin‐dependent pattern formation in the developing embryo. In addition, we show that RCE1 interacts directly with the RING protein RBX1 and is present in a stable complex with SCF. We propose that RBX1 functions as an E3 for RUB modification of CUL1.

  • Received November 22, 2002.
  • Revision received February 19, 2003.
  • Accepted February 27, 2003.
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