Isolation and characterization of genic microsatellites from de novo assembly transcriptome in the bivalve Ruditapes philippinarum

The marine bivalve Ruditapes philippinarum（Veneridae） has always been an economically important aquaculture species. In this study, 106 831 unigenes and 2 664 SSR loci（1 locus/40 sequences）were achieved from the de novo assembly transcriptome. Among all the SSRs, tri-nucleotides（46.40%） was the most, followed by di-nucleotides（32.43%）. Meanwhile, AAC/GTT（19.82%） was the most common SSR loci searched. After polymorphism detection using 32 wild R. philippinarum individuals, 34 polymorphic and 3 monomorphic SSR loci were screened, and the genetic index of them was calculated. The results show that PIC of 30 polymorphic SSR loci was at medium and high levels（PIC>0.25）. However, there were five SSR polymorphic loci（e.g. MG871423, MG871428, MG871429, MG871434, MG871435） deviating from the Hardy-Weinberg equilibrium after the Bonferroni correction（adjusted P=0.001 471）. The Na value（number of alleles per locus） ranged from 2 to 7. In addition, the H_o（observed heterozygosities） and Hc（expected heterozygosities） were 0.100 0-1.000 0 and 0.191 3-0.723 6, respectively. Therefore, RNA-Seq was shown as a fast and cost-effective method for genic SSR development in non-model species. Meanwhile,the 37 loci from R. philippinarum will further enrich the genetic information and advance the population conservation and restoration.