The genetics and genomics of the forage grasses Lolium perenne (perennial ryegrass) and Festuca pratensis (meadow fescue)
Perennial ryegrass (Lolium perenne) is a diploid, outbreeding grass which is the most important forage grass species in temperate areas worldwide; as such, it is the mainstay of grassland-based agricultural systems in many areas of the world. Perennial ryegrass is also frequently a major component of the grass seed mixtures that are used for sports, amenity and other landscape purposes within the UK. As a consequence, it has a significant impact on both the economic life and environmental footprint of the country.
Our work at Aberystwyth has focused on developing genetic, introgression, comparative and physical mapping populations and resources for the analysis of genome composition and the identification of quantitative trait loci (QTL) in L. perenne and Lolium/Festuca hybrid populations.
We have developed a number of perennial ryegrass and ryegrass/fescue genetic mapping populations which have been used both to define evolutionary relationships with other grass and cereal species and also to map traits and QTL to defined genomic regions. Target traits have been associated with flowering time, water soluble carbohydrate accumulation, self-incompatibility, seed-set and fertility, disease resistance and ‘staygreen’ senescence. The genetic map of perennial ryegrass has 7 linkage groups (equivalent to the 7 chromosomes) which have been defined with gene-based SNP markers, SSRs and DArTs.
Hybrid crosses between perennial ryegrass and meadow fescue (Lolium/Festuca) show useful fertility and high levels of intergeneric recombination. This has been exploited to produce and identify all seven possible substitution lines of meadow fescue chromosomes in the perennial ryegrass background. Populations derived from these have been ‘bin-mapped’ using genomic in situ hybridisation (GISH) and genetic markers to define the size and position of introgressed regions. From this it has been possible to define the relative positions of meiotic recombination events on the metaphase chromosomes and to relate these ‘physical’ distances to estimates of genetic distance.
Perennial ryegrass is classified in the sub-family Pooideae, along with the cereals, wheat, barley, rye and oats and the model grass , Brachypodium distachyon. It is slightly more diverged from the other major moncot model (and crop), rice. As part of the process of defining the evolutionary relationships between these species we have been using ‘cross-species’ markers to identify regions of conserved genetic synteny. This allows us to map genes and traits across these various species and to infer gene orders and contents in ryegrass from those already identified in the sequenced models, rice and B. distachyon.
For further information on Comparative Mapping contact Ian Armstead.
We are currently developing a physical map of the L. perenne genome based on high information content fingerprints (HICF) and BAC-end sequences derived from c. 10x coverage of the L. perenne genome – estimated at 2-2.5Gb). Ultimately, this will allow us to define large, physical contigs within the L. perenne genome which can be used for both isolating the genes controlling important traits and in developing a complete sequence of the L. perenne genome. This work is supported by an Industrial Partnership Award from the BBSRC (BB/G012342/1) with financial contributions from Germinal Holdings, Syngenta and ViaLactia Biosciences.