Abstract
BackgroundComparative genome mapping determines the linkage between homologous genes of related taxa. It has already been used in plants to characterize agronomically important genes in lesser studied species, using information from better studied species. In the Maloideae sub-family, which includes fruit species such as apple, pear, loquat and quince, genome co-linearity has been suggested between the genera Malus and Pyrus; however map comparisons are incomplete to date.FindingsGenetic maps for the apple rootstocks 'Malling 9' ('M.9') (Malus × domestica) and 'Robusta 5' ('R5') (Malus × robusta), and pear cultivars 'Bartlett' and 'La France' (Pyrus communis) were constructed using Simple Sequence Repeat (SSR) markers developed from both species, including a new set of 73 pear Expressed Sequence Tag (EST) SSR markers. Integrated genetic maps for apple and pear were then constructed using 87 and 131 SSR markers in common, respectively.The genetic maps were aligned using 102 markers in common, including 64 pear SSR markers and 38 apple SSR markers. Of these 102 markers, 90 anchor markers showed complete co-linearity between the two genomes.ConclusionOur alignment of the genetic maps of two Malus cultivars of differing species origin with two Pyrus communis cultivars confirms the ready transferability of SSR markers from one genus to the other and supports a high level of co-linearity within the sub-family Maloideae between the genomes of Malus and Pyrus.
Highlights
Comparative genome mapping determines the linkage between homologous genes of related taxa
When co-linearity between Malus and Pyrus was examined by comparing maps of the European pears (Pyrus communis) 'Bartlett' and 'La France', and the Japanese pear (Pyrus pyrifolia) 'Housui' with those of apple cultivars (Malus × domestica) 'Fiesta' and 'Discovery' [8] using 66 transferable apple simple sequence repeat (SSR) loci, all the pear linkage groups were aligned to the apple consensus linkage groups with at least one marker in common [9]
Pear Expressed Sequence Tag (EST)-Simple Sequence Repeat (SSR) polymorphism All 73 pear SSR markers developed from pear expressed sequence tags (EST) amplified a PCR product when tested on apple and 29 (40%) were polymorphic in the 'M.9' × 'Robusta 5' (R5)' population (Table 1)
Summary
We have extended the list of SSR markers used for comparative genome mapping in the Maloideae, for Malus and Pyrus. As the apple whole genome sequence will be available soon, we propose that apple should be used as the model for species in the Maloideae and that genetic information can be inferred in the other species by comparison of their genetic maps with that of apple. We suggest that this approach may be extended to include other members of the Rosaceae, such as Prunus, Rubus and Rosa
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