TaVRT2 represses transcription of the wheat vernalization gene TaVRN1

In wheat, VRN1/TaVRN1 and VRN2/TaVRN2 determine the growth habit and flowering time. In addition, the MADS box transcription factor VEGETATIVE TO REPRODUCTIVE TRANSITION 2 (TaVRT2) is also associated with the vernalization response in a manner similar to TaVRN2. However, the molecular relationship between these three genes and their products is unknown. Using transient expression assays in Nicotiana benthamiana, we show that TaVRT2 acts as a repressor of TaVRN1 transcription. TaVRT2 binds the CArG motif in the TaVRN1 promoter and represses its activity in vivo. In contrast, TaVRN2 does not bind the TaVRN1 promoter and has no direct effect on its activity, but it can enhance the repression effect of TaVRT2. This suggests that a repressor complex regulates the expression of TaVRN1. In winter wheat, TaVRT2, TaVRN2 and TaVRN1 transcripts accumulate in the shoot apical meristem and young leaves, and temporal expression is consistent with TaVRT2 and TaVRN2 being repressors of floral transition, whereas TaVRN1 is an activator. Non-vernalized spring wheat grown under a short-day photoperiod accumulates TaVRT2 and shows a delay in flowering, suggesting that TaVRT2 is regulated independently by photoperiod and low temperature. The data presented suggest that TaVRT2, in association with TaVRN2, represses the transcription of TaVRN1.