Wheat SOC1 functions independently of WAP1/VRN1, an integrator of vernalization and photoperiod flowering promotion pathways

Heading time in bread wheat (Triticum aestivum L.) is determined by three characters - vernalization requirement, photoperiodic sensitivity and narrow-sense earliness (earliness per se) - which are involved in the phase transition from vegetative to reproductive growth. The wheat APETALA1 (AP1)-like MADS-box gene, wheat AP1 (WAP1, identical with VRN1), has been identified as an integrator of vernalization and photoperiod flowering promotion pathways. A MADS-box gene, SUPPRESSOR OF OVEREXPRESSION OF CO 1 (SOC1) is an integrator of flowering pathways in Arabidopsis. In this study, we isolated a wheat ortholog of SOC1, wheat SOC1 (WSOC1), and investigated its relationship to WAP1 in the flowering pathway. WSOC1 is expressed in young spikes but preferentially expressed in leaves. Expression starts before the phase transition and is maintained during the reproductive growth phase. Overexpression of WSOC1 in transgenic Arabidopsis plants caused early flowering under short-day conditions, suggesting that WSOC1 functions as a flowering activator in Arabidopsis. WSOC1 expression is affected neither by vernalization nor photoperiod, whereas it is induced by gibberellin at the seedling stage. Furthermore, WSOC1 is expressed in transgenic wheat plants in which WAP1 expression is cosuppressed. These findings indicate that WSOC1 acts in a pathway different from the WAP1-related vernalization and photoperiod pathways.