Molecular characterization of the duplicated meristem identity genes HvAP1a and HvAP1b in barley

The vernalization gene VRN-1 has been identified as a MADS-box transcription factor orthologous to the meristem identity gene APETALA1 (AP1). A single copy of this gene was found in diploid wheat, but 2 copies were reported in barley. In this study, we present a detailed characterization of these 2 copies to understand their respective roles in the vernalization response. We identified 2 groups of barley bacterial artificial chromosomes (BACs), each containing 1 AP1 copy designated hereafter as HvAP1a and HvAP1b. A physical map of the VRN-H1 region showed that the HvAP1a BACs were part of the VRN-H1 region but that the HvAP1b BACs were not. Numerous structural changes were observed between the barley and wheat VRN-1 physical maps. In a population segregating for VRN-H1, the HvAP1a gene cosegregated with growth habit, suggesting that HvAP1a is the barley vernalization gene VRN-H1. The other copy, HvAP1b, was mapped on the centromeric region of chromosome 1H, the chromosome where vernalization gene VRN-H3 was previously mapped. We developed a mapping population segregating for VRN-H3 and showed that 2 molecular makers flanking HvAP1b locus were not linked to growth habit. The HvAP1b copy has a complete deletion of the first 2 exons, suggesting that it is a truncated pseudogene and not a candidate for VRN-H3. In summary, this study contributed a detailed physical map of the barley VRN-H1 region, showed several structural differences with the orthologous wheat region, and clarified the identity of the barley VRN-H1 gene.