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Plant Physiology Preview Published on July 20, 2007; 10.1104/pp.107.102285
OPEN ACCESS ARTICLE
Received May 11, 2007 Genetic Analysis of Sumoylation in Arabidopsis: Heat-induced Conjugation of SUMO1 AND 2 Is Essential
Department of Genetics, 425-G Henry Mall, University of Wisconsin-Madison, Madison, WI 53706-1574 * Corresponding author; email: vierstra{at}wisc.edu.
The post-translational addition of Small-Ubiquitin-Like Modifiers (SUMOs) to other intracellular proteins has been implicated in a variety of eukaryotic functions, including modifying cytoplasmic signal transduction, nuclear import and subnuclear compartmentalization, DNA repair, and transcription regulation. For plants in particular, both genetic analyses and the rapid accumulation of SUMO conjugates in response to various adverse environmental conditions suggest that SUMOylation plays a key role in the stress response. Through genetic analyses of various SUMO conjugation mutants, we show here that the SUMO1 and 2 isoforms in particular and SUMOylation in general are essential for viability in Arabidopsis thaliana. Null T-DNA insertion mutants affecting the single genes encoding the SUMO-activating enzyme subunit SAE2 and the SUMO-conjugating enzyme SCE1 are embryonic lethal, with the arrest occurring early in embryo development. Whereas the single genes encoding the SUMO1 and SUMO2 isoforms are not essential by themselves, double mutants missing both are also embryonic lethal. Viability can be restored by reintroduction of SUMO1 expression in the homozygous sum1-1 sum2-1 background. Various stresses like heat shock dramatically increase the pool of SUMO conjugates in planta. This increase involves SUMO1 and 2 and is mainly driven by the SUMO-protein ligase SIZ1, with most of the conjugates accumulating in the nucleus. Taken together, it appears that SIZ1-mediated conjugation of SUMO1 and 2 to other intracellular proteins is essential in Arabidopsis, possibly through stress-induced modification of a potentially diverse pool of nuclear proteins.
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