A potential role of UBC28 interacting RING finger protein TaRF1 in spike development of wheat

RING finger proteins are the most abundant proteins in plants and may be essential for diverse aspects of cellular regulation in plant growth and development. Many RING finger proteins are E3 ubiquitin ligases, which play important roles in protein-protein interactions and ubiquitin-dependent protein degradation. The TaRF1 gene encodes a novel RING finger protein. In this study, we characterized the wheat (Triticum aestivum) RING finger domain as a hexapoid wheat ubiquitin ligase. To study the role of TaRF1 in wheat, we isolated TaRF1 from wheat spike cDNA. TaRF1 was 756 bp and encoded a putative 251-amino-acid with a predicted molecular mass of 28.57 kDa and isoelectric point of 5.75. A typical C3HC4-type RING finger domain was found at the C-terminal region of the TaRF1 protein. TaRF1 expression was investigated in the developmental stages and under various stresses by using reverse transcription polymerase chain reaction and was confirmed by subcellular localization of TaRF1 labeled with green fluorescent protein. Using the yeast 2-hybrid screen, we identified potential TaRF1-interacting proteins in a wheat spike library. Among the 8 clones that were identified as potential interacting partners of TaRF1 using yeast 2-hybrid screening, we found the strongest interaction between TaRF1 and the ubiquitin E2 enzyme TaUBC28 in tobacco leaves through biomolecular fluorescence complementation. The selectivity of interactions between E2 enzymes and RING E3 ligases represents a central and crucial part of the ubiquitin-conjugation pathways in organisms. These results indicate that the TaRF1 protein can interact with TaUBC28 in vitro and in vivo.