Conservation Of Microsatellite Loci Research Articles

Construction of Microsatellite Linkage Maps for Corymbia

AbstractThe genus Corymbia is closely related to the genus Eucalyptus, and like Eucalyptus contains tree species that are important for sub-tropical forestry. Corymbia’s close relationship with Eucalyptus suggests genetic studies in Corymbia should benefit from transfer of genetic information from its more intensively studied relatives. Here we report a genetic map for Corymbia spp. based on microsatellite markers identified de novo in Corymbia sp or transferred from Eucalyptus. A framework consensus map was generated from an outbred F2population (n = 90) created by crossing two unrelated Corymbia torelliana × C. citriodora subsp. variegata F1trees. The map had a total length of 367 cM (Kosambi) and was composed of 46 microsatellite markers distributed across 13 linkage groups (LOD 3). A high proportion of Eucalyptus microsatellites (90%) transferred to Corymbia. Comparative analysis between the Corymbia map and a published Eucalyptus map identified eight homeologous linkage groups in Corymbia with 13 markers mapping on one or both maps. Further comparative analysis was limited by low power to detect linkage due to low genome coverage in Corymbia, however, there was no convincing evidence for chromosomal structural differences because instances of non-synteny were associated with large distances on the Eucalyptus map. Segregation distortion was primarily restricted to a single linkage group and due to a deficit of hybrid genotypes, suggesting that hybrid inviability was one factor shaping the genetic composition of the F2population in this inter-subgeneric hybrid. The conservation of microsatellite loci and synteny between Corymbia and Eucalyptus suggests there will be substantial value in exchanging information between the two groups.

Applicability of rabbit microsatellite primers for studies of hybridisation between an introduced and a native hare species.

Introduced species may hybridise with relatives in the native fauna or flora and thereby compete for matings and transmit alien DNA. Such interference may contaminate unique genepools, disturb existing ecological balances and may ultimately result in the extinction of the native species. In Sweden, the introduced brown hare (Lepus europaeus Pall.) hybridise with the native mountain hare (L. timidus L.), both relatively common members of the present Swedish fauna. This hybridisation has resulted in the transmission of mitochondrial DNA from the mountain hare to the brown hare, but absence of species differences in karyotype and allozymes have prevented investigations of the amount of nuclear gene flow. More polymorphic genetic markers are needed to analyse evidence of hybridisation in the nuclear genome. The conservation of microsatellite loci across taxa usually enables PCR amplification of microsatellites in closely related species with the same primers. We have used five microsatellite primer pairs, developed for the European wild rabbit (Oryctolagus cuniculus L.) to amplify microsatellites in the two species of hare in Sweden. The obtained allelic variation was used to construct a genetic distance tree based on the amount of shared alleles between all pairs of individuals (shared-allele index). This method offered sufficient differences to arrange all individuals in two groups, one for each species. Identification of individual hybrids based on the number of alleles shared between the species is not possible with these five microsatellite markers.

Conservation and synteny of SSR loci and QTLs for vegetative propagation in four Eucalyptus species.

Conservation of microsatellite loci, heterozygous in Eucalyptus grandis, Eucalyptus urophylla, Eucalyptus tereticornis and Eucalyptus globulus, allowed us to propose homeologies among genetic linkage groups in these species, supported by at least three SSR loci in two different linkage groups. Marker-trait associations for sprouting and adventitious rooting ability were also compared in the four species. Putative quantitative trait loci (QTLs) influencing vegetative propagation traits were located on homeologous linkage groups. Our findings indicate high transferability of microsatellite markers between Eucalyptus species of the Symphyomyrtus subgenus and establish foundations for the use of synteny in the genetic analysis of this genus. Microsatellite markers should help integrate eucalypt genetic linkage maps from various sources. The availability of comparative linkage maps provides a basis of more-efficient use of genetic information for molecular breeding and evolutionary studies in Eucalyptus.

Conservation of microsatellite loci within the genus Vitis

Eleven microsatellites isolated from grapevine (Vitis vinifera) were used to study the degree of conservation of these sequences across different Vitis species. Nine microsatellites were newly isolated, the remaining two (VVS2 and VVS5) came from the literature. A preliminary assay on the conservation of priming sites was carried out on 14 non-V. vinifera species, including relevant taxa for breeding. Parthenocissus quinquefolia was added as representative of a related genus. Cross-species amplification was obtained in 94% of the 176 genotype×locus tested combinations. Three microsatellite loci were then cloned and sequenced in ten species. The microsatellite repeat was found present in all cases. The repeat region was often longer in V. vinifera than in the other species. Furthermore the non-source species showed interruptions in the repeat. In spite of these constraints, which could reduce the polymorphism of microsatellites in non-source species, the results demonstrate the possibility of extending the use of microsatellite markers to wild germplasm and inter-specific hybrids. Point mutations have been found in microsatellite flanking regions and these variations have been used to investigate the genetic relationship among taxa. The Neighbor-joining tree that was obtained on the basis of ten nucleotide variations, showed that there is not a clear cut difference between American, Asian and European species and that the actual taxonomy which reflects the geographical distribution of species must most likely be revised. Moreover, in general, nucleotide variations which occur in microsatellite flanking regions provide new molecular tools for investigating the evolution of species.

Conservation of Microsatellite Loci across Species of Artiodactyls: Implications for Population Studies

DNA microsatellites have proven useful as markers in studies of gene mapping due to their high level of polymorphism and broad genomic distribution. These properties suggest that they also will be useful for studies of population structure. The limiting factor is the development of polymerase chain reaction (PCR) primer sets for each new species of interest, as this requires the construction and screening of libraries of genomic DNA, DNA sequencing, and design of primers. The locations and sequences of some microsatellites have been shown to be conserved across species of mammals. We tested these markers in an array of closely related species of bovids and cervids. PCR primer pairs designed for bovine, ovine, or caprine microsatellite loci successfully amplified microsatellites in many other species of artiodactyls. When 20 primer sets were tested on 10 species of bovids and six species of cervids, polymorphic products were obtained for seven or more of the 16 species with 12 of the primer pairs. This success in using heterologous PCR primers to amplify microsatellite loci in several different species eliminates the need to develop new sets of primers for each species and therefore facilitates the use of DNA microsatellites as markers in studies of population genetics. The primers tested here form a suite of useful markers for studies of artiodactyls that contains more polymorphic loci than any existing set of allozyme or RFLP loci.