Microsatellite DNA in Actinidia chinensis: isolation, characterisation, and homology in related species

We have isolated and sequenced 263 microsatellite-containing clones from tw o small insert libraries of Actinidia chinensis enriched for (AC/GT) and (A G/CT) repeats, respectively. Primer pairs were designed for 203 microsatell ite loci and successfully amplified from both plasmid and A. chinensis geno mic DNA. In this paper we report the sequences of 40 primer pairs for which we have demonstrated Mendelian segregation in the progeny from controlled crosses. The polymorphism of ten microsatellites of each type was evaluated in four diploid and six tetraploid genotypes of A. chinensis. All microsat ellites proved to be polymorphic, the number of alleles per locus detected in polyacrylamide sequencing gels ranging from 9 to 17. The high degree of polymorphism in Actinidia renders these markers useful either for mapping i n A. chinensis or for fingerprinting cultivars of both domesticated kiwifru it species (A. chinensis and A. deliciosa). While most primer pairs produce d single amplification products, about 20% generated banding patterns consi stent with the amplification of two different loci. This supports the hypot hesis that diploid species of Actinidia (2n = 2x = 58) are polyploid in ori gin with a basic chromosome number x = 14/15 and that chromosome duplicatio n may have occurred during the evolution of the genus. Finally, we have ass ayed the cross-species transportability of primer pairs designed from A. ch inensis sequences and have found extensive cross-species amplification with in the genus Actinidia; 75% of primer pairs gave successful amplification i n the eight species assayed (A. arguta, A. rufa, A. polygama, A. chrysantha , A. callosa, A. hemsleyana, A. eriantha, and A. deliciosa), which are repr esentative of the four sections into which the genus is currently split.