[Homologous simple sequence repeats (SSRs) analysis in tetraploid (AD1) and diploid (A₂, D₅) genomes of Gossypium].

Simple sequence repeats (SSRs)are a class of repetitive DNA sequences, which are commonly used for genome analysis. Comparison of the homologous SSRs among different genomes is helpful to understand the evolutionary process in relative species. In this study, SSR scanning was performed to investigate their distribution and length variation among the genomes of G. raimondii (D₅), G. arboretum (A₂) and G. hirsutum (AD₁). The results demonstrated that the distribution of SSRs in A genome was very similar with that in D genome, while the length variation of homologous SSRs between A and AD genome was more conserved than that between D and AD genome. Compared with SSRs in AD genome, the number of SSRs with longer motif length in A genome was about five times of those with shorter motif length, while it was about three times in D genome. This implied that the length variation rates of homologous SSRs between diploid cotton and tetraploid cotton were different during the parallel evolution due to the subgenome fusion, and the motif length of most SSRs in tetraoploid genome tended to become shorter than homologous SSRs in diploid genome during the process of evolution. This study comprehensively compared the SSRs in three cotton genomes and revealed the significant difference among them, providing a foundation for further evolutionary study of Gossypium genome.