<i>VERNALIZATION2</i> alters early tiller development in a facultative spring hexaploid bread wheat

An extended period of cold exposure enables the process of vernalization in winter cereals and is important for the synchronised timing of the floral transition. The cereal-specific floral repressor VERNALIZATION2 (VRN2) has an integral role in vernalization, yet this locus remains poorly characterised in facultative spring hexaploid wheat, Triticum aestivum. Through the generation of defined germplasm combined with bespoke experimental protocols, which enable a realistic simulation of annual field-based UK growth conditions, we were able to distinguish gene expression and phenotypic differences at the subgenomic level of VRN2 in hexaploid bread wheat. Our research in a facultative wheat suggests that the tandemly duplicated genes comprising the VRN2 locus, ZCCT1 and ZCCT2, have gene expression patterns that respond to multiple environmental factors. These genes also show coregulation, forming a regulatory loop between ZCCT-D1 and ZCCT-D2. The function of these genes beyond the classic vernalization response is explored in a facultative wheat. Here, we identified that VRN-D2 regulates early tiller development, with an accelerated rate of secondary tiller emergence and presence of coleoptile tillers. The findings identify that the VRN2 loci in bread wheat are formed of multiple genes, which have not only overlapping but also unique regulation and function. Selecting these genes individually may offer a route to alter wheat plant architecture without directly impacting vernalization requirement.