Heterogeneous Expression and Purification of the Wheat VRN1 K-Box Domain Suggest the Formation of a Tetramer of the VRN1 Protein

In cereal species such as wheat (Ttiticum aestivum) and barley (Hordeum vulgare), many studies have indicated that VERNALIZATION 1 (VRN1) functions as a flowering promoter, which activates florigen gene expression. The wheat florigen gene Wheat FLOWERING LOCUS T (WFT, which is identical to VRN3) is an integrator of the vernalization, photoperiod and autonomous pathways in wheat flowering, and the WFT expression is correlated with the VRN1 expression. VRN1 encodes an APETALA1/FRUITFULL-like MADS-box transcription factor which expression is induced by vernalization, leading to flowering thorough up-regulation of WFT. In Arabidopsis, it has been reported that protein-protein interactions are keys for MADS-box protein function and MADS-box transcription factors must dimerize to bind to the target gene. In this study, by using gel permeation chromatography (GPC) with purified VRN1 protein, we indicated the possibility that VRN1 protein exists as tetramer-like as flowering homeotic MADS-box proteins in Arabidopsis.