Plant Science 180 (2011) 775–782 Contents lists available at ScienceDirect Plant Science journal homepage: www.elsevier.com/locate/plantsci Overexpression of OsRDCP1, a rice RING domain-containing E3 ubiquitin ligase, increased tolerance to drought stress in rice (Oryza sativa L.) Hansol Bae a,1 , Sung Keun Kim a,1 , Seok Keun Cho a , Bin Goo Kang b , Woo Taek Kim a,∗ a Department of Systems Biology, College of Life Science and Biotechnology, Yonsei University, Seoul 120-749, Republic of Korea b ReSEAT Program, Korea Institute of Science and Technology Information, Seoul 130-741, Republic of Korea article info Article history: Received 5 February 2011 Received in revised form 21 February 2011 Accepted 21 February 2011 Available online 4 March 2011 Keywords: Drought stress E3 ubiquitin ligase Oryza sativa OsRDCP1-overexpressing lines Rice osrdcp1 knock-out mutant RING domain abstract CaRma1H1 was previously identified as a hot pepper drought-induced RING E3 Ub ligase. We have identi- fied five putative proteins that display a significant sequence identity with CaRma1H1 in the rice genome database (http://signal.salk.edu/cgi-bin/RiceGE). These five rice paralogs possess a single RING motif in their N-terminal regions, consistent with the notion that RING proteins are encoded by a multi-gene family. Therefore, these proteins were named OsRDCPs (Oryza sativa RING domain-containing proteins). Among these paralogs, OsRDCP1 was induced by drought stress, whereas the other OsRDCP members were constitutively expressed, with OsRDCP4 transcripts expressed at the highest level in rice seedlings. osrdcp1 loss-of-function knockout mutant and OsRDCP1-overexpressing transgenic rice plants were developed. Phenotypic analysis showed that wild-type plants and the homozygous osrdcp1 G2 mutant line displayed similar phenotypes under normal growth conditions and in response to drought stress. This may be due to complementation by other OsRDCP paralogs. In contrast, 35S:OsRDCP1 T2 transgenic rice plants exhib- ited improved tolerance to severe water deficits. Although the physiological function of OsRDCP1 remains unclear, there are several possible mechanisms for its involvement in a subset of physiological responses to counteract dehydration stress in rice plants. © 2011 Elsevier Ireland Ltd. All rights reserved. 1. Introduction Turnover of a wide range of eukaryotic proteins is regulated by the ubiquitin (Ub)-26S proteasome pathway. This pathway plays a critical role in the control of multiple cellular processes as diverse as cell cycle, differentiation, hormone responses, protein trafficking, and responses to environmental stresses [1–3]. Multiple Ub chains are attached to the target proteins by E1, E2, and E3 enzymes and serve as degradation tags, leading to the proteolysis of targeted proteins by the 26S proteasome complex [4,5]. Based on subunit composition, E3s can be classified into two groups. The HECT and RING/U-box E3 classes are comprised of single subunits, whereas the SCF and anaphase-promoting-complex (APC) E3 ligases consist of multiple polypeptides [1–5]. In most cases, E3 Ub ligases are responsible for identifying specific target proteins. Abbreviations: ABA, abscisic acid; MeJA, methyl jasmonate; RT-PCR, reverse transcriptase-polymerase chain reaction; SA, salicylic acid; Ub, ubiquitin. ∗ Corresponding author. Tel.: +82 2 2123 2661; fax: +82 2 312 5657. E-mail address: wtkim@yonsei.ac.kr (W.T. Kim). 1 These two authors equally contributed to this work and are listed in alphabetical order. A number of RING-containing proteins function as E3 Ub ligases in responses to abiotic environmental stresses. Arabidopsis HOS1 works as a negative regulator for cold-stress signal transduction [6,7], while XERICO participates positively in salt- and osmotic- stress responses through the overproduction of abscisic acid (ABA) [8]. Arabidopsis SDIR1 and DRIP RING E3 Ub ligases are involved in the regulation of positive and negative drought-stress responses, respectively [9,10]. Ryu et al. [11] recently reported that AtAIRP1 RING E3 is a positive regulator of an ABA-dependent defense mech- anism against drought stress. Compared to the studies of Arabidopsis RING E3 ligases, research elucidating the roles of these Ub ligases in crop plants has been scarce. The hot pepper CaRma1H1 RING E3 ligase confers strong tolerance to dehydration stress when it is ectopically expressed in Arabidopsis [12]. More recently, the rice OsDSG1 RING protein was reported to regulate high-salt and drought stress responses [13]. Collectively, these results are indicative of cellular functions of RING E3 Ub ligases in defense against abiotic environmental stresses in higher plants. We aimed to unravel the physiological roles of RING E3 Ub lig- ases with respect to abiotic stresses, such as water deficit. In this report, we used rice as a molecular genetic model system and identified five homologous OsRDCP (Oryza sativa RING domain- containing protein) family members, all of which contain a single 0168-9452/$ – see front matter © 2011 Elsevier Ireland Ltd. All rights reserved. doi:10.1016/j.plantsci.2011.02.008