The UNUSUAL FLORAL ORGANS gene of Arabidopsis thaliana is an F-box proteinrequired for normal patterning and growth in the floral meristem

Genetic and molecular studies have suggested that the UNUSUAL FLORAL ORGANS (UFO) gene, from Arabidopsis thaliana, is expressed in all shoot apical me ristems, and is involved in the regulation of a complex set of developmenta l events during floral development, including floral meristem and floral or gan identity. Results from in situ hybridization using genes expressed earl y in floral development as probes indicate that UFO controls growth of youn g floral primordia. Transgenic constructs were used to provide evidence tha t UFO regulates floral organ identity by activating or maintaining transcri ption of the class B organ-identity gene APETALA 3, but not PISTILLATA. In an attempt to understand the biochemical mode of action of the UFO gene pro duct, we show here that UFO is an F-box protein that interacts with Arabido psis SKP1-like proteins, both in the yeast two-hybrid system and in vitro. In yeast and other organisms both F-box proteins and SKP1 homologues are su bunits of specific ubiquitin E3 enzyme complexes that target specific prote ins for degradation. The protein selected for degradation by the complex is specified by the F-box proteins. It is therefore possible that the role of UFO is to target for degradation specific proteins controlling normal grow th patterns in the floral primordia, as well as proteins that negatively re gulate APETALA 3 transcription.