Identification of dynamin as an interactor of rice GIGANTEA by tandem affinity purification (TAP).

GIGANTEA (GI), CONSTANS (CO) and FLOWERING LOCUS T (FT) regulate photoperiodic flowering in Arabidopsis. In rice, OsGI, Hd1 and Hd3a were identified as orthologs of GI, CO and FT, respectively, and are also important regulators of flowering. Although GI has roles in both flowering and the circadian clock, our understanding of its biochemical functions is still limited. In this study, we purified novel OsGI-interacting proteins by using the tandem affinity purification (TAP) method. The TAP method has been used effectively in a number of model species to isolate proteins that interact with proteins of interest. However, in plants, the TAP method has been used in only a few studies, and no novel proteins have previously been isolated by this method. We generated transgenic rice plants and cell cultures expressing a TAP-tagged version of OsGI. After a two-step purification procedure, the interacting proteins were analyzed by mass spectrometry. Seven proteins, including dynamin, were identified as OsGI-interacting proteins. The interaction of OsGI with dynamin was verified by co-immunoprecipitation using a myc-tagged version of OsGI. Moreover, an analysis of Arabidopsis dynamin mutants indicated that although the flowering times of the mutants were not different from those of wild-type plants, an aerial rosette phenotype was observed in the mutants. We also found that OsGI is present in both the nucleus and the cytosol by Western blot analysis and by transient assays. These results indicate that the TAP method is effective for the isolation of novel proteins that interact with target proteins in plants.