Abstract
Ubiquitination and sumoylation are essential post-translational modifications that regulate growth and development processes in plants, including control of hormone signaling mechanisms and responses to stress. This study showed that COP1 (Constitutive photomorphogenic 1) regulated the activity of Arabidopsis E3 SUMO (Small ubiquitin-related modifier) ligase AtSIZ1 through its E3 ubiquitin ligase activity. Yeast two hybrid analysis demonstrated that COP1 and AtSIZ1 directly interacted with one another, and subcellular localization assays indicated that COP1 and AtSIZ1 co-localized in nuclear bodies. Analysis of ubiquitination showed that AtSIZ1 was polyubiquitinated by COP1. The AtSIZ1 level was higher in cop1-4 mutants than in wild-type seedlings under light or dark conditions, and overexpression of a dominant-negative (DN)-COP1 mutant led to a substantial increase in AtSIZ1 accumulation. In addition, under drought, cold, and high salt conditions, SUMO-conjugate levels were elevated in DN-COP1-overexpressing plants and cop1-4 mutant plants compared to wild-type plants. Taken together, our results indicate that COP1 controls responses to abiotic stress by modulation of AtSIZ1 levels and activity.
Highlights
As sessile organisms, plants are unable to control or avoid their surrounding environment
This study showed that COP1 modulated AtSIZ1 levels via its E3 ubiquitin ligase activity and, in turn, modulation of AtSIZ1 levels affected the sumoylation of target proteins involved in the response to abiotic stresses
Previous research focused on characterizing the functions of COP1 in light signaling, and several transcription factors and photoreceptors were shown to be negatively regulated by COP1
Summary
Plants are unable to control or avoid their surrounding environment. Plants need to adapt to their environment by responding appropriately to stress and modulating their developmental programs. Many fine-tuning mechanisms are involved in adaptive changes, and, of these, the modification of translated proteins by the attachment of molecules such as ubiquitin, SUMO (Small ubiquitin-related modifier), and phosphate and methyl groups is thought to be a rapid and efficient way to cope with environment changes. Ubiquitination is a post-translational modification in which ubiquitin is covalently attached to a target protein by the activities of three enzymes: E1, E2, and E3 (Hochstrasser, 1996). Two different ubiquitination pathways have been reported to date. Monoubiquitination, a single ubiquitin molecule is attached to a target protein
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