Abstract
SUMO (small ubiquitin-related modifier) conjugation (sumoylation) to protein substrates is a reversible posttranslational modification that regulates signaling by modulating transcription factor activity. The SUMO conjugation cycle involves activation (E1), conjugation (E2), and ligation (E3) steps. SUMO conjugation to transcription factors in animals and yeast facilitates transcription factor activation or repression, chromatin modifications and subnuclear partitioning. Our research established that Arabidopsis SIZ1 is a SUMO E3 ligase, which facilitates ligation of SUMO1/2 to proteins in the final step of the conjugation cycle, and has been implicated in hormonal and environmental stress signaling, including ABA response, phosphate starvation response, and basal thermotolerance. SIZ1-dependent sumoylation controls adaptation to low and high temperature extremes, and ABA response. To control cold signaling and ABA signaling, SIZ1 mediates sumoylation of ICE1 and ABI5, respectively. The function of sumoylation in plant response to abiotic stresses will be discussed.
