Identification and characterization of microsatellites in Norway spruce (Picea abies K.)

Norway spruce (Picea abies) genomic libraries were screened for presence of dinucleotide AC/GT and AG/CT microsatellites (or simple sequence repeats). On average, one (AG)n microsatellite every 194 kb and one (AC)n microsatellite every 406 kb were found. Forty-six positive clones were sequenced and primers flanking 24 AG microsatellites and 12 AC microsatellites designed. Only seven (20%) of them produced the expected single-locus polymorphic pattern when used to amplify Norway spruce DNAs. The other primer pairs gave either multiple bands or bad amplification, or a single monomorphic fragment. Such a small proportion of successful primer pairs was attributed to the high level of complexity of the Norway spruce genome. Dot blot analysis of the clones showed that many of them contained repetitive DNA and that those giving the single-locus polymorphic patterns usually corresponded to single-copy sequences. A family of repetitive DNA that contained AG repeats was identified and was present in about 40 000 copies per haploid genome. Simple Mendelian inheritance was observed for all the polymorphisms tested. The average number of alleles was 13, ranging from 6 to 22, and the expected heterozygosity was 0.79 when seven microsatellites were used to genotype a panel of 18 trees representing different populations. Compared with isozymes, microsatellites are about five times more informative and could provide an extremely valuable source of markers for genome mapping and genetic diversity studies.Key words: microsatellite, repetitive DNA, hypervariability, Picea abies, genome complexity.