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ABSTRACT: The covalent addition of Small Ubiquitin-Related Modifier (SUMO) to various intracellular proteins is an essential regulatory step in most eukaryotes. Due to its necessity and the large number of putative targets, SUMO is thought to be second only to ubiquitin (Ub) among Ub-fold proteins in terms of regulatory influence. Whereas, ubiquitylation (i.e., the attachment of Ub) is generally associated with protein degradation, SUMOylation appears to have more diverse consequences, including the regulation of transcription, chromatin structure/accessibility, nuclear import, and various protein-protein interactions, and even appears to block the action of Ub by competing for the same binding sites on targets. Paramount to understanding SUMO function(s) is knowing the complete catalog of SUMO targets. In the following addendum we review our recent publication describing the proteomic identification of SUMO substrates in the model plant, Arabidopsis thaliana, and expand our analyses with regard to the changes in SUMOylation patterns that are induced by heat stress. Collectively, our data indicate that SUMOylation is highly dynamic with evidence that SUMO addition globally modifies transcription and chromatin accessibility, especially during stress.
Plant signaling & behavior 01/2011; 6(1):130-3.
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ABSTRACT: The covalent attachment of SUMO (small ubiquitin-like modifier) to other intracellular proteins affects a broad range of nuclear processes in yeast and animals, including chromatin maintenance, transcription, and transport across the nuclear envelope, as well as protects proteins from ubiquitin addition. Substantial increases in SUMOylated proteins upon various stresses have also implicated this modification in the general stress response. To help understand the role(s) of SUMOylation in plants, we developed a stringent method to isolate SUMO-protein conjugates from Arabidopsis thaliana that exploits a tagged SUMO1 variant that faithfully replaces the wild-type protein. Following purification under denaturing conditions, SUMOylated proteins were identified by tandem mass spectrometry from both nonstressed plants and those exposed to heat and oxidative stress. The list of targets is enriched for factors that direct SUMOylation and for nuclear proteins involved in chromatin remodeling/repair, transcription, RNA metabolism, and protein trafficking. Targets of particular interest include histone H2B, components in the LEUNIG/TOPLESS corepressor complexes, and proteins that control histone acetylation and DNA methylation, which affect genome-wide transcription. SUMO attachment site(s) were identified in a subset of targets, including SUMO1 itself to confirm the assembly of poly-SUMO chains. SUMO1 also becomes conjugated with ubiquitin during heat stress, thus connecting these two posttranslational modifications in plants. Taken together, we propose that SUMOylation represents a rapid and global mechanism for reversibly manipulating plant chromosomal functions, especially during environmental stress.
Proceedings of the National Academy of Sciences 09/2010; 107(38):16512-7. · 9.68 Impact Factor
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ABSTRACT: The posttranslational 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 SUMO2 isoforms, in particular, and SUMOylation, in general, are essential for viability in Arabidopsis (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 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 SUMO2 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 SUMO2 to other intracellular proteins is essential in Arabidopsis, possibly through stress-induced modification of a potentially diverse pool of nuclear proteins.
Plant physiology 10/2007; 145(1):119-34. · 6.53 Impact Factor
