Parental origin and genomic evolution of tetraploid Gossypium species by molecular marker and GISH analyses

摘要

Polyploidy is a common phenomenon that has played a significant role in the evolutionary history of angiosperms. The allopolyploid Gossypium species (AD-genome) is the result of hybridization between two diploid species (A-genome and D-genome). In order to further explore the possible A- and D-genome donor of extant tetraploid cotton species, two molecular markers (random amplified polymorphic DNA [RPAD] and simple sequence repeat [SSR]) were employed on 13 cotton species including nine diploid (two A-genome and seven D-genome) and four tetraploid cotton species (AD-genome). Genomic in situ hybridization (GISH) was also used to further confirm the genomic origin and organization of tetraploid cotton species. The result showed that 26 of 40 RAPD primers and 49 of 120 SSR primers were polymorphic by 65% and 40.8% respectively. Clustering analyses for RAPD and SSR results indicated that the genome of G. raimondii is the nearest to the D-subgenome of tetraploid species, and it may be the ancestral D-genome donor of the tetraploid cotton. Because of the greatest genetic similarity coefficient between G. herbaceum and G. arboreum, two A-genome diploid species are phylogenetically equidistant from extant tetraploid cotton. GISH using one parental gDNA from A- or D-genome as a labeled probe together with an excess of another as blocking DNA, and tetraploid cotton as target, was found to a superior method for clearly distinguishing between two putative parental genomes. The phylogenetic and GISH results in this paper supported the hypothesis that the donors of the parental genomes are sisters of G. arboreum or G. herbaceum and G. raimondii and provided direct evidence for the origin and monophyly of the polyploidy Gossypium species.