RESEARCH ARTICLE Characterization of the Ubiquitin- Conjugating Enzyme Gene Family in Rice and Evaluation of Expression Profiles under Abiotic Stresses and Hormone Treatments

Ubiquitin-conjugating enzyme E2s (UBCs), which catalyze the transfer of ubiquitin to sub-strate or E3 ligases, are key enzymes in ubiquitination modifications of target proteins. How-ever, little is known about the knowledge of UBC gene family in rice. In this study, a total of 39 UBC encoding genes, which all contained an UBC domain with a cysteine active site, were identified in the rice genome. These were classified into fifteen distinct subfamilies based upon their sequence similarity and phylogenetic relationships. A subset of 19OsUBC genes exhibited chromosomal duplication; 4 and 15OsUBC genes were tandemly and seg-mentally duplicated, respectively. Comprehensive analyses were performed to investigate the expression profiles ofOsUBC genes in various stages of vegetative and reproductive de-velopment using data from EST, Microarrays, MPSS, and real-time PCR. ManyOsUBC genes exhibited abundant and tissue-specific expression patterns. Moreover, 14OsUBCs were found to be differentially expressed under treatments with drought, or salt stresses. The expression analysis after treatments with IAA, 6-BA, GA and ABA indicated that almost allOsUBC genes were responsive to at least two of the four hormones. Several genes were significantly down-regulated under all of the hormone treatments, and most of the genes re-duced by 6-BA were also reduced by GA. This study will facilitate further studies of the OsUBC gene family and provide useful clues for functional validation ofOsUBCs in rice