An Arabidopsis SUMO E3 Ligase, SIZ1, Negatively Regulates Photomorphogenesis by Promoting COP1 Activity

• Published in: PLOS genetics Vol. 12; no. 4; p. e1006016
• Main Authors: 三浦 謙治, Lin Xiao-Li, Niu De, Hu Zi-Liang, Kim Dae Heon, Jin Yin Hua, Cai Bin, Liu Peng, Miura Kenji, Yun Dae-Jin, Kim Woe-Yeon, Lin Rongcheng, Jin Jing Bo
• Format: Journal Article
• Language: English
• Published: United States Public Library of Science 01.04.2016; Public Library of Science (PLoS)
• Subjects: Amino Acid Substitution - genetics; Amino acids; Arabidopsis; Arabidopsis - genetics; Arabidopsis - growth & development; Arabidopsis Proteins - genetics; Arabidopsis Proteins - metabolism; Arabidopsis thaliana; Basic-Leucine Zipper Transcription Factors - genetics; Basic-Leucine Zipper Transcription Factors - metabolism; Biology and life sciences; Cell cycle; Gene Expression Regulation, Plant; Genetic aspects; Genetic research; Homeostasis; Kinases; Ligases; Ligases - genetics; Ligases - metabolism; Light; Mutation; Nuclear Proteins - genetics; Nuclear Proteins - metabolism; Photomorphogenesis; Physiological aspects; Plant Development - genetics; Post-translational modifications; Proteins; Proteolysis; Research and Analysis Methods; Seedlings - genetics; Seedlings - growth & development; Small Ubiquitin-Related Modifier Proteins - genetics; Small Ubiquitin-Related Modifier Proteins - metabolism; Sumoylation - genetics; Ubiquitin; Ubiquitin-Protein Ligases - genetics; Ubiquitin-Protein Ligases - metabolism; Ubiquitination - genetics
• DOI: 10.1371/journal.pgen.1006016
• ISSN: 1553-7404; 1553-7390

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.