Transferability of cereal EST-SSR markers to ryegrass

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Abstract
A large number of expressed sequence tags (ESTs) in public databases have provided an opportunity for the systematic development of simple sequence repeat (SSR) markers. EST-SSRs derived from conserved coding sequences show considerable cross-species transferability in related species. In the present study, we assessed the utility of cereal EST-SSRs in ryegrass (Lolium spp.). A total of 165 cereal EST-SSRs were tested; a high rate of transferability (57%) and polymorphism (67% of functional EST-SSRs) was demonstrated between cereals and ryegrass. A total of 46 segregating loci derived from 37 EST-SSRs were mapped on an existing ryegrass genetic map. The mapped loci were uniformly distributed across all seven linkage groups without significant clustering at the distal regions of linkage groups. Sequences of ryegrass amplicons generated by randomly selected 16 EST-SSRs were aligned with reference sequences of cereal EST-SSRs. The SSR motifs and repeat lengths of the cereal EST-SSR markers were different from the majority of ryegrass amplicons. Furthermore, a majority of EST-SSRs amplified different flanking sequences of SSRs in ryegrass than the original cereal sequences. Our results suggest that the high degree of cereal EST-SSR transferability to ryegrass can be a useful enhancement to the molecular database of PCR-based markers but sequence analysis is essential before transferring genetic information using comparative mapping.