Phylogeny of the genus Gossypium and genome origin of its polyploid species inferred from variation in nuclear repetitive DNA sequences

Abstract

Knowledge of phylogenetic relationships among taxa is essential for comparative and evolutionary genomic research. Here, we report reconstruction of the phylogenetic tree of the genus Gossypium containing cultivated cottons of importance in agriculture by using variation of nuclear repetitive DNA sequences. Genomic DNA was isolated from 87 available accessions of 35 species representing all eight basic genome groups of the genus Gossypium and analyzed to infer phylogeny of the genus and genome origin of its polyploid species. Twenty-two interspersed repeated sequence clones derived from G. hirsutum, each representing a repeated sequence family, were hybridized to the genomic DNA of the 35 species, respectively. Southern hybridization showed that 15 of the repetitive DNA sequences could be detected in all of the eight diploid genome groups, five were A genome-specific, and two were detected in some of the non D-genome groups. A total of 642 major restriction bands of repeated sequences were used for phylogenetic analysis of the species. A phylogenetic tree of the species was constructed, based on the parsimony method and evaluated by the bootstrap approach. The tree was consistent with those previously constructed with different methods in major clades in which the genealogical lineages of species are largely congruent with genome designations and geographical distribution; but significantly different branching among some of the species was observed. These results not only further confirm the previously phylogenetic analysis of the species and the utility of repetitive DNA sequences for phylogenetic analysis of the genus Gossypium, but also provide new insights into the phylogeny of the genus.