Vol.:(0123456789) 1 3 Planta (2021) 253:126 https://doi.org/10.1007/s00425-021-03647-8 SHORT COMMUNICATION Critical role of cysteine‑266 of SIE3 in regulating the ubiquitination and degradation of SIP1 transcription factor in Lotus japonicus Ping Wu 1  · Yong Feng 1  · Zhongmin Zou 1  · Yangrong Cao 1  · Songli Yuan 2 Received: 24 February 2021 / Accepted: 20 May 2021 / Published online: 25 May 2021 © The Author(s), under exclusive licence to Springer-Verlag GmbH Germany, part of Springer Nature 2021 Abstract Main conclusion A conserved cysteine residue (C266)-mediated homo-dimerization of SIE3 is required for the ubiq- uitination and degradation of SIP1 transcription factor in Lotus japonicas Abstract CTLH/CRA/RING-containing proteins have been shown to possess E3-ligase activities and are crucial for the regulation of numerous cellular signaling pathways. In our previous studies, SIE3 (SymRK-Interacting E3 ubiquitin ligase), a CTLH/CRA/RING-containing protein from Lotus japonicus, has been shown to associate with both Symbiosis Receptor Kinase (SymRK) and SIP1 (SymRK interacting protein 1) transcription factor, and ubiquitinate SymRK (Yuan et al. Plant Physiol 160 (1):106–117, 2012; Feng et al. Front Plant Sci 11: 795, 2020). Besides, we previously also demonstrated that the residue, cysteine-266 in the CRA (CT11-RanBPM) domain is required for homodimerization of SIE3 and cysteine-266 residue-mediated homodimerization is important for the symbiosic function of SIE3 (Feng et al. 2020). In this report, SIE3 was shown to induce the ubiquitination and degradation of SIP1. The cysteine-266 residue is essential for the E3-ligase activity and is highly conserved in the SIE3-like proteins. Our works refned the working model that homodimerization of SIE3 is required for ubiquitin-related degradation of SIP1 and found a conserved cysteine residue plays a key role in the activity of a plant dimeric E3 ligase. Keywords CTLH/CRA/RING-containing protein · Dimeric E3 ligase · E3 ligase activity · SIE3-C266 · Ubiquitinated substrate Abbreviations CRA CT11-RanBPM CTLH C-terminal to LisH GID Glucose-induced degradation defcient SIE3 SymRK-Interacting E3 ubiquitin ligase SIP1 SymRK interacting protein 1 SymRK Symbiosis Receptor Kinase Introduction Ubiquitination is an important post-translational modifca- tion of proteins and is involved in regulation of a spectrum of cell events (Grabbe et al. 2011). Ubiquitination is specifc to eukaryotes, and this process involves a series of enzymes, including activating enzyme (E1), conjugating enzyme (E2) and ubiquitin ligase (E3) (Li et al. 2018). Among them, E1 and E2 enzymes act as activated ubiquitin tags, while E3 determines the specifcity of ubiquitination targets, so a pre- cise mechanism of how E3 enzymes perform their enzymatic activity is paramount to understand how the ubiquitination process is regulated. The glucose-induced degradation defcient (GID) com- plex, which contains multiple subunits, is an evolutionarily conserved E3 ligase in saccharomyces cerevisiae (Liu and Pfrrmann 2019) and the C-terminal to LisH (CTLH) com- plex is the homologue of the GID complex in mammalian (Hufman et al. 2019). The GID/CTLH complex has been widely studied in regulating multiple biological processes, Communicated by Dorothea Bartels. * Yangrong Cao yrcao@mail.hzau.edu.cn * Songli Yuan songliyuan@caas.cn; yyyyy-0909@163.com 1 State Key Laboratory of Agricultural Microbiology, Huazhong Agricultural University, Wuhan 430070, China 2 Key Laboratory of Biology and Genetic Improvement of Oil Crops, Ministry of Agriculture and Rural Afairs of PRC, Oil Crops Research Institute of Chinese Academy of Agriculture Sciences, Wuhan 430062, China