The major loci controlling vernalization requirement in the diploid wheat Triticum monococcum are VRN1 and VRN2 (in cereals the VERNALIZATION, VRN, designation applies to genes conferring a vernalization requirement and differs from Arabidopsis genes of the same name that are involved in vernalization response). These two genes have strong epistatic interactions and are likely to be part of the same regulatory pathway. VRN1 is located on wheat chromosome 5. Genes controlling vernalization requirement in barley and rye map to syntenic regions, as judged by their co-segregation with common markers, indicating that related genes control vernalization requirement in these different cereals.
[...] Short-day Vernalization While vernalization is the acquisition or acceleration of the ability to flower following a chilling treatment, a similar effect has been observed by exposing some plants, like wheat and barley, to SDs. Flowering of wheat and barley is promoted in response to LDs; spring varieties and vernalized winter varieties generally accelerate flowering in response to LDs. However, the response of unvernalized winter varieties today length is less consistent. Some winter varieties of wheat and barley display earlier flowering if growth in SDs precedes transfer to LD conditions. [...]
[...] As vernalization requirement in barley maps to positions syntenic with VRN1 and VRN2 known as Sgh2 and Sgh1, respectively or VRN-H1 and VRN-H2, this indicates that vernalization requirement involves related genes in wheat and barley and that differences between winter and spring habit involved mutation of similar genes. A gene homologous to VRN2 (ZCCT1) is present in a collinear region of winter barley and can be identified by DNA hybridization using ZCCT1 as a probe. Vernalization Response Progress towards the characterization of the molecular basis of vernalization response has so far depended on induced mutations and the analysis of natural variation in this trait. [...]
[...] Connecting cold to vernalization While we have recently acquired insight into the molecular basis of vernalization requirement and response, a fundamental gap in our knowledge remains the elucidation of how cold is perceived and signaled to factors that execute vernalization. Although work with Arabidopsis has recently shed light on the process of cold acclimation, which prepares the plant to withstand cold, there is little to indicate that this cold response connects with vernalization. First, cold acclimation is a short-term response that is not remembered after return to warmer conditions. [...]
[...] Therefore on the basis of map position, expression pattern in response to vernalization and promoter sequence differences between spring and winter wheat accessions, this MADSbox protein was putatively identified as VRN1. Caveats to the definitive identification of this gene as VRN1 remain: it has not yet proved possible to generate complete physical coverage of the chromosomal region flanked by markers that co-segregate with the VRN1 phenotype; no loss-offunction VRN1 mutation has been described that might reveal a phenotype consistent with a role in flowering-time control; and no functional or causal connection between the promoter deletions and an effect on VRN1 regulation by VRN2 has yet been established. [...]
[...] The Arabidopsis VRN genes are involved in mediating the vernalization response, and as such are distinct functionally and genetically from the wheat VRN genes. VRN1 and VRN2 act to stably repress FLC upon the transition to warm temperatures in vrn1 and vrn2 mutants FLC expression begins to rise when plants are returned to warm conditions rather than remaining low as it would in a wild-type plant. VRN1 encodes a B3 DNA–binding protein and VRN2 encodes a Polycombgroup protein. The VRN2- related protein from Drosophila, Su(z)12, functions as part of a chromatin- remodelling complex that induces H3K9 methylation. [...]
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