COP1 (CONSTITUTIVE PHOTOMORPHOGENIC 1), a ubiquitin E3 ligase, is a central negative regulator of photomorphogenesis. However, how COP1 activity is regulated by post-translational modifications remains largely unknown. Here we show that SUMO (small ubiquitin-like modifier) modification enhances COP1 activity. Loss-of-function siz1 mutant seedlings exhibit a weak constitutive photomorphogenic phenotype. SIZ1 physically interacts with COP1 and mediates the sumoylation of COP1. A K193R substitution in COP1 blocks its SUMO modification and reduces COP1 activity in vitro and in planta. Consistently, COP1 activity is reduced in siz1 and the level of HY5, a COP1 target protein, is increased in siz1. Sumoylated COP1 may exhibits higher transubiquitination activity than does non-sumoylated COP1, but SIZ1-mediated SUMO modification does not affect COP1 dimerization, COP1-HY5 interaction, and nuclear accumulation of COP1. Interestingly, prolonged light exposure reduces the sumoylation level of COP1, and COP1 mediates the ubiquitination and degradation of SIZ1. These regulatory mechanisms may maintain the homeostasis of COP1 activity, ensuing proper photomorphogenic development in changing light environment. Our genetic and biochemical studies identify a function for SIZ1 in photomorphogenesis and reveal a novel SUMO-regulated ubiquitin ligase, COP1, in plants.
|Original language||English (US)|
|State||Published - Apr 29 2016|
Bibliographical noteKAUST Repository Item: Exported on 2020-10-01
Acknowledgements: This work was supported by grants 31170170 and 31471363, from the National Natural Science Foundation of China (http://www.nsfc.gov.cn/), to JBJ. This work was also supported by grant 2012CB114302, from the Ministry of Science and Technology of the People’s Republic of China (http://www.most.gov.cn/eng/), and by grant XDA08010105, from the Chinese Academy of Sciences (http://www.cas.cn/), to JBJ. The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.