Seok Keun Cho received his Ph.D. in Plant systems biology from Yonsei University, South Korea. At present he is working as a Research Professor at Institute of Life Science and Biotechnology and BrainKorea21 Plus initiative for Biological function & Systems, Yonsei University, Korea.
An important way of plant defense against environmental and pathogen stresses is exploiting a controlled protein turnover pathway, the ubiquitin proteasome system (UPS). E3 ligases are key enzymes that play a central role in target determing by the UPS. Recently, it has been defined that U-box ligases, a specific class of E3 ligases, are largly implicated in the defence mechanisms against abiotic and biotic stresses in many plants. However, no studies on U-box E3 ligases have been performed in barley, one of the important staple crops in the world. In this study, we identified 68 putative U-box E3 ligases from the barley genome and corresponding expressed sequence tags (ESTs) data. Based on their domain compositions and arrangement, we classified barley U-box proteins into eight different classes. Similar to Arabidopsis and rice U-box E3 ligases, most of barley U-box E3 ligases have evolutionary well-conserved domain organizations. We identified a barley specific U-box gene with a GABA transporter 1 (GTA1) domain in addition to U-box domain, which is neither found in Arabidopsis nor in rice. Furthermore, we found that the expressions of some U-box genes were specifically up-and-down regulated by drought stress or by pathogen infection, implying the possible roles of barley U-box genes in stress responses. The identification and classification of barley U-box genes may provide a plaftorm to functionally study the stress-related E3 ligases in barley