Regions associated with repression of the barley (Hordeum vulgare) VERNALIZATION1 gene are not required for cold induction

Activity of the VERNALIZATION1 (VRN1) gene is required for flowering in temperate cereals such as wheat and barley. In varieties that require prolonged exposure to cold to flower (vernalization), VRN1 is expressed at low levels and is induced by vernalization to trigger flowering. In other varieties, deletions or insertions in the first intron of the VRN1 gene are associated with increased VRN1 expression in the absence of cold treatment, reducing or eliminating the requirement for vernalization. To characterize natural variation in VRN1, the first intron of the barley (Hordeum vulgare) VRN1 gene (HvVRN1) was assayed for deletions or insertions in a collection of 1,000 barleys from diverse geographical regions. Ten alleles of HvVRN1 containing deletions or insertions in the first intron were identified, including three alleles that have not been described previously. Different HvVRN1 alleles were associated with differing levels of HvVRN1 expression in non-vernalized plants and with different flowering behaviour. Using overlapping deletions, we delineated regions in the HvVRN1 first intron that are associated with low levels of HvVRN1 expression in non-vernalized plants. Deletion of these intronic regions does not prevent induction of HvVRN1 by cold or the maintenance of increased HvVRN1 expression following cold treatment. We suggest that regions within the first intron of HvVRN1 are required to maintain low levels of HvVRN1 expression prior to winter but act independently of the regulatory mechanisms that mediate induction of HvVRN1 by cold during winter.