Macromolecular organization and genetic mapping of a rapidly evolving chromosome-specific tandem repeat family (B77) in cotton (Gossypium).
Isolation and characterization of the most prominent repetitive element families in the genome of tetraploid cotton (Gossypium barbadense L; [39]) revealed a small subset of families that showed very different properties in tetraploids than in their diploid progenitors, separated by 1-2 million years. One element, B77, was characterized in detail, and compared to the well-conserved 5S and 45S rRNA genes. The 572 bp B77 repeat was found to be concentrated in several discontinuous tandem arrays confined to a single 550 kb SalI fragment in tetraploid cotton. Genetic mapping based on the absence of the pentameric 'rung' in the G. barbadense 'ladder' showed that B77 maps to a D-subgenome chromosome. In situ hybridization supports the contention that the array is confined largely to a single chromosomal site in the D-subgenome. The B77 repeat has undergone a substantial increase in copy number since formation of tetraploid cotton from its diploid relatives. RFLPs observed among tetraploid cotton species suggest that amplification and/or rearrangement of the repeat may have continued after divergence of the five tetraploid cotton species. B77 contains many short direct repeats and shares significant DNA sequence homology with a Nicotiana alata retrotransposon Tna1-2 integrase motif. The recent amplification of B77 on linkage group D04 suggests that the D-subgenome of tetraploid cotton may be subject to different evolutionary constraints than the D-genome diploid chromosomes, which exhibit few genome-specific elements. Further, the abundance of B77 in G. gossypioides supports independent evidence that it may be the closest extant relative of the D-genome ancestor of cotton.
Zhao
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Department of Soil and Crop Sciences, Texas A&M University, College Station 77843-2474, USA.
Ji
Y
Y
Ding
X
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Stelly
D M
DM
Paterson
A H
AH
D001483:Base Sequence; D002874:Chromosome Mapping; D018744:DNA, Plant / Q000737:chemistry / Q000235:genetics; D004171:Diploidy; D019143:Evolution, Molecular; D017343:Genes, Plant; D008040:Genetic Linkage; D005819:Genetic Markers; D003368:Gossypium / Q000235:genetics*; D008969:Molecular Sequence Data; D005810:Multigene Family; D011123:Polyploidy; D012091:Repetitive Sequences, Nucleic Acid
D018744:DNA, Plant; D005819:Genetic Markers