Chromosomal dispositions were analyzed on the metaphase plate of tetraploid cotton (AADD). At metaphase, the two subgenomes, A and D, were separated in a radial pattern in which the small D subgenome chromosomes tended to concentrate at the center and the large A subgenome chromosomes were scattered about the periphery on the metaphase plate. Although the ordered chromosome arrangement was disturbed in an artificial hexaploid (AADDGG), the separation pattern could be recovered after the majority of the additional genome (GG) chromosomes were removed by backcrossing the artificial hexaploid with the tetraploid cotton (AADD). A similar genome separation phenomenon was also found in synthesized tetraploid cotton (AAGG). These results indicate that the genome separation pattern could be established immediately after tetraploid cotton formation and could be stably inherited in tetraploid cotton. Given the evidence of parental genome separation in other plants and animals, we speculated that genome separation might be a normal phenomenon in diploid and polyploid species. These finding will shed light on the chromosome conformation in plant cells.Significance Statement
Chromosomes usually occupy defined places in the nucleus, consistent with the idea that spatial and temporal organization is important for gene expression and genome maintenance. Here we show that the two subgenomes in tetraploid cotton are separated in a radial pattern at metaphase.