Mining,characterization, and exploitation of EST-derived microsatellites in <Emphasis Type="Italic">Gossypium barbadense</Emphasis>

Simple sequence repeats (SSRs) have been widely applied as molecular markers in genetic studies. However, the number of ex-pressed sequence tags (ESTs) and SSR markers from Gossypium barbadense is fewer than those from other cotton species. In this study, EST-SSR distribution from G. barbadense was characterized and new G. barbadense-derived EST-SSR markers were de-termined on the basis of the ESTs obtained by randomly sequencing 2 cDNA libraries associated with fiber development in G. barbadense. By mining 9697 non-redundant ESTs, a total of 638 SSR loci derived from 595 ESTs were observed. In G. barba-dense, the frequency of ESTs containing SSRs was 6.13%, with an average of 1 SSR in every 10.4 kb of EST sequence. Further-more, trinucleotide was found to be the most abundant repeat type among 2–6-nucleotide repeat types. It accounted for 26.6% of the total, followed by the hexanucleotide (26.0%) and pentanucleotide repeats (25.9%). Among all the repeat motifs, (AAG)n accounted for the highest proportion. EST-SSR primer pairs were developed using the Primer3 program, and the redundant primers were removed using the virtual PCR approach. As a result, 380 non-redundant EST-SSR primer pairs were developed and used to detect polymorphisms between the mapping parents G. hirsutum ‘TM-1’ and G. barbadense ‘Hai7124’ for constructing linkage groups in cultivated allotetraploid cotton. Out of these, 98 (25.8%) primer pairs detected polymorphisms. Finally, 95 polymorphic loci from 82 primer pairs were integrated into the backbone genetic map; of these, 42 were mapped into the A subgenome and 53 into the D subgenome. The present work provided the foundation for constructing saturated genetic maps and conducting comparative genomic studies on different cotton species.