EST-SSR markers identification based on RNA-sequencing and application in Schisandra chinensis

Background: Schisandra chinensis, a climbing woody vine, is the best-known and representative genus of the Schisandraceae family which is an important plant in Chinese herbal medicine; however, the application of molecular breeding is restricted by the few genetic markers for this species. Results: In this study, we performed transcriptome sequencing of S. chinensis using the Illumina HiSeq platform to establish a library of expressed sequence tag-simple sequence repeat (EST-SSR) markers. A total of 59,786 unigenes were obtained and 6254 putative SSR sites were detected with a frequency of 10.46%. The predominant type of repeat motif was dinucleotide (35.71%), followed by trinucleotide (13.22%), hexanucleotide (0.50%), tetranucleotide (0.06%), and pentanucleotide (0.22%). We randomly selected 50 EST-SSR primer pairs and used 14 of these for genetic diversity analysis in 42 S. chinensis genotypes. All 42 accessions were successfully identified and formed four major clusters, indicating that the SSR markers can be used for genetic diversity analysis and genetic linkage map construction. In addition, using the polymorphic bands associated with 10 markers as DNA fingerprints, we generated a manual cultivar identification diagram that can distinguish between the 42 accessions, with different individuals identifiable based on polymorphic band patterns. Conclusion: S. chinensis transcriptome data is an effective resource for developing SSR markers. These results can provide a basis for the identification of S. chinensis accessions and construction of genetic linkage maps as part of future selective breeding and conservation efforts for this valuable plant.