VRN2 is a gene involved in flower repressing during the vernalization response in wheat (and other cereals). It works by repressing VRN1, a gene responsible for flowering competency and response. This kind of relationship between VRN1 and VRN2 is called an epistatic relationship because VRN2 masks the expression of VRN1 during long (and warm) days and then a shift occurs and VRN2 is reduced during cold, short days, therby derepressing VRN1 which causes flowering competency in the shoot apical meristem.
VRN2 in wheat is located on chromosome 5A but there are paralogs scattered throughout the genome. The location of the gene also depends on which organism you are looking at. The majority of research on this gene has been done by agricultural researchers who have focused on the crown pooid group (including wheat, barley and oats). Not much is known about when this gene evolved in the phylogenetic history and how many rounds of duplications in each lineage this gene has been though. The idea exists that a shift from tropical to temperate climate was a catalyst for the evolution of the VRN gene group.
Something very interesting to note about the vernalization mechanism in plants is that the commonly researched plant, Arabidopsis thaliana (and lyrata) have a different mechanism of vernalization that involves a completely different suite of proteins that are not homologs of the VRN genes. Schematic here
Allelic differences are one of the driving factors of the variation in vernalization response and it has been shown that differences in the VRN1 first intron is directly related to that change. (Yan et al., 2003, 2004a; Fu et al., 2005; von Zitzewitz et al., 2005; Szu ̈ cs et al., 2006b). This suggests the first intron is relatively conserved and that it may be involved with regulation of the transcription of the gene.
As of right now, no one knows where VRN2 arose in the phylogeny of grasses and if it evolved at the same time as the vernalization response.
Mutation of this gene leads to vernalization insensitivity and gives you crop lines that can be planted in spring and flower later that spring (Yan et al. 2006; Bonnin et al. 2008; Distelfeld et al. 2009).
Understanding the genetic mechanism behind the vernalization response can hopefully help us better deal with changes in climate change and it's affects on our crop flowering times.
For more information see:
Allard, V., Veisz, O., Kõszegi, B., Rousset, M., Le Gouis, J., & Martre, P. (2012). The quantitative response of wheat vernalization to environmental variables indicates that vernalization is not a response to cold temperature. Journal of experimental botany, 63(2), 847–57. doi:10.1093/jxb/err316
Finnegan, E. J., Sheldon, C. C., Jardinaud, F., Peacock, W. J., & Dennis, E. S. (2004). A Cluster of Arabidopsis Genes with a Coordinate Response to an Environmental Stimulus, 14, 911–916. doi:10.1016/j
Greenup, A. G., Sasani, S., Oliver, S. N., Walford, S. a, Millar, A. a, & Trevaskis, B. (2011). Transcriptome analysis of the vernalization response in barley (Hordeum vulgare) seedlings. PloS one, 6(3), e17900. doi:10.1371/journal.pone.0017900
Preston, J. C., & Kellogg, E. a. (2008). Discrete developmental roles for temperate cereal grass VERNALIZATION1/FRUITFULL-like genes in flowering competency and the transition to flowering. Plant physiology, 146(1), 265–76. doi:10.1104/pp.107.109561
Below: Figures of geneious alignments of wheat and barley VRN2 homologs.