The objective of this study was to map quantitative trait loci (QTL) for the vernalization response in perennial ryegrass (Lolium perenne L.). The mapping population consisted of 184 F2 genotypes produced from a cross between one genotype of a synthetic perennial ryegrass variety "Veyo" and one genotype from the perennial ryegrass ecotype "Falster". Veyo and Falster were chosen among four different populations because of their contrasting vernalization requirements. In total, five QTL for the vernalization response, measured as days to heading, were identified and mapped to linkage groups (LG) LG2, LG4, LG6 and LG7. Individually, these QTL explained between 5.4 and 28.0% of the total phenotypic variation. The overall contribution of these five QTL was 80% of the total phenotypic variation. A putative orthologue of Triticum monococcum VRN1 was amplified from genomic DNA from perennial ryegrass. PCR fragments covering the proximal part of the promoter and the 5' end of the orthologue were subsequently PCR-amplified from both parents of the mapping population and shown to possess 95% DNA sequence identity to VRN1. Several polymorphisms were identified between Veyo and Falster in this fragment of the putative VRN1 orthologue. A CAPS marker, vrn-1, was developed and found to co-segregate with a major QTL on LG4 for the vernalization response. This indicates that the CAPS marker vrn-1 could be located in an orthologous gene of the wheat VRN1.

Whole-genome sequences established for model and major crop species constitute a key resource for advanced genomic research. For outbreeding forage and turf grass species like ryegrasses (Lolium spp.), such resources have yet to be developed. Here, we present a model of the perennial ryegrass (Lolium perenne) genome on the basis of conserved synteny to barley (Hordeum vulgare) and the model grass genome Brachypodium (Brachypodium distachyon) as well as rice (Oryza sativa) and sorghum (Sorghum bicolor). A transcriptome-based genetic linkage map of perennial ryegrass served as a scaffold to establish the chromosomal arrangement of syntenic genes from model grass species. This scaffold revealed a high degree of synteny and macrocollinearity and was then utilized to anchor a collection of perennial ryegrass genes in silico to their predicted genome positions. This resulted in the unambiguous assignment of 3,315 out of 8,876 previously unmapped genes to the respective chromosomes. In total, the GenomeZipper incorporates 4,035 conserved grass gene loci, which were used for the first genomewide sequence divergence analysis between perennial ryegrass, barley, Brachypodium, rice, and sorghum. The perennial ryegrass GenomeZipper is an ordered, information-rich genome scaffold, facilitating map-based cloning and genome assembly in perennial ryegrass and closely related Poaceae species. It also represents a milestone in describing synteny between perennial ryegrass and fully sequenced model grass genomes, thereby increasing our understanding of genome organization and evolution in the most important temperate forage and turf grass species.