Post-translational modifications of Arabidopsis E3 SUMO ligase At SIZ1 are controlled by environmental conditions.

Sumoylation regulates numerous cellular functions in plants as well as in other eukaryotic systems. However, the regulatory mechanisms controlling E3 small ubiquitin-related modifier ( SUMO) ligase are not well understood. Here, post-translational modification of the Arabidopsis E3 SUMO ligase At SIZ1 was shown to be specifically controlled by abiotic stresses. At SIZ1 ubiquitination was induced by exposure to heat stress in transgenic plants overexpressing the E3 ubiquitin ligase COP1. In addition, At SIZ1 ubiquitination was strongly enhanced in transgenic plants overexpressing SUMO isopeptidase ESD4 under heat stress. By contrast, drought stress induced sumoylation rather than ubiquitination of At SIZ1 and sumoylated forms of At SIZ1 accumulated in esd4 and cop1-4 mutants. Moreover, siz1 mutants were found to be tolerant to heat and drought stresses. Taken together, these results indicate that ubiquitination and sumoylation of At SIZ1 in response to abiotic stresses depend on the activities of COP1 and ESD4 and that the activity and stability of At SIZ1 can be specifically controlled by different abiotic stresses. [ABSTRACT FROM AUTHOR]