351 J. Crop Sci. Biotech. 2017 (December) 20 (5) : 351 ~ 357 DOI No. 10.1007/s12892-017-0104-0 RESEARCH ARTICLE Functional Diversity of RING E3 Ligases of Major Cereal Crops in Response to Abiotic Stresses Sandeep Chapagain, Yong Chan Park, Cheol Seong Jang * 1 Plant Genomics Laboratory, Department of Applied Plant Sciences, Kangwon National University, Chuncheon 24341, Korea Received: August 14, 2017 / Revised: October 24, 2017 / Accepted: November 20, 2017 Ⓒ Korean Society of Crop Science and Springer 2017 Abstract Abiotic stresses significantly reduce the grain yield and productivity of cereal crops, especially rice, and this may affect food security in the future. Different abiotic stress adaptation pathways have been investigated and depicted in plants. Among these, the ubiquitin-proteasome system (UPS) has been studied as a key mechanism to understand the protein regulation pathways that enhance the adaptation and survival of plants under various environmental stresses such as drought, salinity, cold, and toxic metalloid exposure. RING E3 ligases constitute a highly diverse and important enzyme group that acts within the 26S UPS, and it also plays a crucial role as a central regulator of plant physiological and cellular processes. This review aimed to highlight recent findings and discoveries regarding the different stress-induced RING E3 ligase genes of major cereal crops and their functions via ubiquitination pathways under different environmental stress conditions. Such genes regulate different physiological responses including protein stabilization, cell membrane integrity, regulation of stomatal opening, and the maintenance of meristematic cells, and they also regulate reactive oxygen species and heavy metal levels via ubiquitination in plants. Hence, the ubiquitination process is considered a potential target for the development of abiotic stress-tolerant crops, and it might be used as an excellent mechanism for stress-tolerant crop improvement programs. Key words : Abiotic stress, cereal crop, RING E3 ligase, ubiquitination, 26S proteasome Cheol Seong Jang () Email: csjang@kangwon.ac.kr Tel: +82332506416, Fax: +82332595558 The Korean Society of Crop Science Introduction Abiotic stresses such as extreme temperatures (frost, cold, and heat), flooding or water logging, drought (water deficit), salinity, and metal and metalloid toxicity adversely impact crop germination, growth, development, and seed quality (Shahbaz and Ashraf 2013). It is estimated that abiotic stresses lead to an average yield loss of up to 60% for most major crop plants (Bray et al. 2000). Furthermore, worldwide food production needs to be doubled by the year 2050 to meet the demands of the growing population. Therefore, development of new stress-tolerant crop varieties could be one of the best ways to ensure food security and safety for many years to come. To survive under various stress conditions, plants have evolved complex mechanisms to perceive external signals and respond to changing environmental conditions. These mechanisms include stress perception, signal transduction, transcriptional activation of stress responsive target genes, and stress-related synthesis of proteins or other molecules that help plants cope with adverse conditions via biochemical and physiological manifestations (Zhu 2016). Recently, studies have focused more on the mechanisms of environmental stress responses that can be genetically engineered to develop stress-tolerant crops. The zinc finger, a small protein structural motif where cysteines (Cys) and/or histidines (His) are coordinated by one or more zinc atoms (Takatsuji 1998) are generally thought to accomplish various functions during interactions with other molecules. Within zinc finger proteins, really interesting new gene (RING) finger proteins belong to a large protein family (Chasapis and Spyoulias 2009). The RING finger domain was firstly identified as a protein structural domain with a novel, cysteine-rich sequence motif. The canonical sequence of the RING domain is Cys-X2 -Cys-X (9-39) -Cys-X (1-3) -HisX (2-3) -Cys- X 2 -Cys-X (4-8) -Cys-X 2 -Cys, where X is any amino acid that can bind to two zinc atoms (Freemont et al. 1991). Based on the presence of Cys or His at the fifth amino position, RING