Abstract
Two bacterial artificial chromosome (BAC) clones (350B21 and 299N22) of Pima 90-53 cotton [Gossypium barbadense Linnaeus, 1753 (2n=4x=52)] were screened from a BAC library using SSR markers. Strong hybridization signals were detected at terminal regions of all A genome (sub-genome) chromosomes, but were almost absent in D genome (sub-genome) chromosomes with BAC clone 350B21 as the probe. The results indicate that specific sequences, which only exist at the terminal parts of A genome (sub-genome) chromosomes with a huge repeat number, may be contained in BAC clone 350B21. When utilizing FISH with the BAC clone 299N22 as probe, a pair of obvious signals was detected on chromosome 13 of D genome (sub-genome), while strong dispersed signals were detected on all A genome (sub-genome) chromosomes. The results showed that peculiar repetitive sequence, which was distributed throughout all A genome (sub-genome) chromosomes, may exist in BAC clone 299N22. The absence of the repetitive sequences, which exist in the two BAC clones, in D genome may account for the genome-size variation between A and D genomes. In addition, the microcolinearity analysis of the clone 299N22 and its homologous region on Gossypium raimondii Ulbrich, 1932 chromosome 13 (D513) indicated that the clone 299N22 might come from A sub-genome of sea island cotton (Gossypium barbadense), and a huge number of small deletions, illegitimate recombination, translocation and rearrangements may have occurred during the genus evolution. The two BAC clones studied here can be used as cytological markers but will be also be helpful to research in cotton genome evolution and comparative genomics.
Highlights
Cotton (Gossypium Linnaeus, 1753) provides an excellent model system for studies on polyploidization, genomic organization, and genome-size variation (Wang et al 2010)
The G. arboreum genome sequence was downloaded from Cotton Genome Project (CGP: http://cgp.genomics.org.cn)
Obvious signals were detected on terminal parts of all G. barbadense Linnaeus, 1753 (A2D2, 2n=4x=52) A sub-genome chromosomes with bacterial artificial chromosome (BAC) clone 350B21 as probe
Summary
Cotton (Gossypium Linnaeus, 1753) provides an excellent model system for studies on polyploidization, genomic organization, and genome-size variation (Wang et al 2010). The latest research shows that the genome size of an A genome species is larger than that of a D genome species (Wang et al 2012; Li et al 2014) Many influential factors, such as polyploidization (Wendel 2000), transposable element amplification (Bennetzen 2002; Kidwell et al 2002; Piegu et al 2006), tandem repeat expansion (Ellegren et al 2002; Morgante et al 2002), gene duplication (Zhang 2003), organellar transfer to the nucleus (Shahmuradov et al 2003), and intron size expansion (Deutsch et al 1999; Vinogradov et al 1999) are thought to be collectively responsible for the genome-size variation (Grover et al 2007). The studies on genome-size differences between A and D genomes will help in understanding cotton evolution as well as facilitating genetic improvement of cotton
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