The CArG-Box Located Upstream from the Transcriptional Start of Wheat Vernalization Gene VRN1 Is Not Necessary for the Vernalization Response
In diploid wheat (Triticum monococcum), and likely in other Triticeae species, the VRN1 gene is essential for the initiation of the reproductive phase, and therefore, a detailed characterization of its regulatory regions is required to understand this process. A CArG-box (MADS-box–binding site) identified in the VRN1 promoter upstream from the transcription initiation site has been proposed as a critical regulatory element for the vernalization response. This hypothesis was supported by the genetic linkage between CArG-box natural deletions and dominant Vrn1 alleles for spring growth habit and by physical interactions with VRT2, a MADS-box protein proposed as a putative flowering repressor regulated by vernalization. Here, we describe a T. monococcum accession with a strong vernalization requirement and a 48-bp deletion encompassing the CArG-box in the VRN1 promoter. Genetic analyses of 2 segregating populations confirmed that this VRN1 allele is completely linked with a strong winter growth habit (vrn-Am1b). Transcript levels of the VRN1 allele with the 48-bp deletion were very low in unvernalized plants and increased during vernalization to levels similar to those detected in other wild-type vrn-Am1 alleles. Taken together, these results indicate that the CArG-box found upstream of the VRN1 transcription initiation site is not essential for the vernalization response.