The study reports the positional cloning of the wheat vernalization gene VRN1, which is essential for the vernalization response in diploid wheat Triticum monococcum. VRN1 is completely linked to MADS-box genes AP1 and AGLG1, located in a 0.03-cM interval flanked by genes Cysteine and Cytochrome B5. No additional genes were found in the 324-kb Triticum monococcum sequence or in the colinear regions of rice and sorghum. Wheat AP1 and AGLG1 genes are similar to Arabidopsis meristem identity genes AP1 and AGL2, respectively. AP1 transcription is regulated by vernalization in both apices and leaves, with a progressive increase in AP1 transcription consistent with the progressive effect of vernalization on flowering time. Vernalization is required for AP1 transcription in winter wheat but not in spring wheat. AGLG1 transcripts are detected during spike differentiation but not in vernalized apices or leaves, suggesting that AP1 acts upstream of AGLG1. No differences were detected between genotypes with different VRN1 alleles in the AP1 and AGLG1 coding regions, but three independent deletions were found in the promoter region of AP1. These results suggest that AP1 is a better candidate for VRN1 than AGLG1. Epistatic interactions between VRN1 and VRN2 suggest a model in which VRN2 represses the expression of AP1. A mutation in the promoter region of AP1 would result in the lack of recognition of the repressor and a dominant spring growth habit. Winter wheats differ from spring wheats in their requirement for a long period at low temperatures to become competent to flower. This process, vernalization, prevents the damage of the cold-sensitive flowering meristem during the winter. VRN1 and VRN2 are the main genes involved in the vernalization response in diploid wheat. Most variation in vernalization requirement in economically important polyploid wheat species is controlled by the VRN1 locus. VRN1 is critical for polyploid wheats' adaptation to autumn sowing and divides wheat varieties into winter and spring market classes. The VRN1 gene has been mapped in colinear regions of the long arm of chromosomes 5A, 5B, and 5D. This region of wheat chromosome 5 is colinear with a region from rice chromosome 3 that includes the HD-6 quantitative trait locus for heading date. However, VRN1 and HD-6 are different genes. Despite progress in elucidating the vernalization pathway in Arabidopsis, little progress has been made in characterizing wheat vernalization genes. The two main genes involved in the vernalization pathway in Arabidopsis, FRI and FLC, have no clearThe study reports the positional cloning of the wheat vernalization gene VRN1, which is essential for the vernalization response in diploid wheat Triticum monococcum. VRN1 is completely linked to MADS-box genes AP1 and AGLG1, located in a 0.03-cM interval flanked by genes Cysteine and Cytochrome B5. No additional genes were found in the 324-kb Triticum monococcum sequence or in the colinear regions of rice and sorghum. Wheat AP1 and AGLG1 genes are similar to Arabidopsis meristem identity genes AP1 and AGL2, respectively. AP1 transcription is regulated by vernalization in both apices and leaves, with a progressive increase in AP1 transcription consistent with the progressive effect of vernalization on flowering time. Vernalization is required for AP1 transcription in winter wheat but not in spring wheat. AGLG1 transcripts are detected during spike differentiation but not in vernalized apices or leaves, suggesting that AP1 acts upstream of AGLG1. No differences were detected between genotypes with different VRN1 alleles in the AP1 and AGLG1 coding regions, but three independent deletions were found in the promoter region of AP1. These results suggest that AP1 is a better candidate for VRN1 than AGLG1. Epistatic interactions between VRN1 and VRN2 suggest a model in which VRN2 represses the expression of AP1. A mutation in the promoter region of AP1 would result in the lack of recognition of the repressor and a dominant spring growth habit. Winter wheats differ from spring wheats in their requirement for a long period at low temperatures to become competent to flower. This process, vernalization, prevents the damage of the cold-sensitive flowering meristem during the winter. VRN1 and VRN2 are the main genes involved in the vernalization response in diploid wheat. Most variation in vernalization requirement in economically important polyploid wheat species is controlled by the VRN1 locus. VRN1 is critical for polyploid wheats' adaptation to autumn sowing and divides wheat varieties into winter and spring market classes. The VRN1 gene has been mapped in colinear regions of the long arm of chromosomes 5A, 5B, and 5D. This region of wheat chromosome 5 is colinear with a region from rice chromosome 3 that includes the HD-6 quantitative trait locus for heading date. However, VRN1 and HD-6 are different genes. Despite progress in elucidating the vernalization pathway in Arabidopsis, little progress has been made in characterizing wheat vernalization genes. The two main genes involved in the vernalization pathway in Arabidopsis, FRI and FLC, have no clear