Individual chromosome assignment and chromosomal collinearity in Gossypium thurberi, G. trilobum and D subgenome of G. barbadense revealed by BAC-FISH

Abstract

The experiment on individual chromosome assignments and chromosomal diversity was conducted using a multi-probe fluorescence in situ hybridization (FISH) system in D subgenome of tetraploid Gossypium barbadense (D_b), G. thurberi (D₁) and G. trilobum (D₈), which the later two were the possible subgenome donors of tetraploid cottons. The FISH probes contained a set of bacterial artificial chromosome (BAC) clones specific to 13 individual chromosomes from D subgenome of G. hirsutum (D_h), a D genome centromere-specific BAC clone 150D24, 45S and 5S ribosomal DNA (rDNA) clones, respectively. All tested chromosome orientations were confirmed by the centromere-specific BAC probe. In D₁ and D₈, four 45S rDNA loci were found assigning at the end of the short arm of chromosomes 03, 07, 09 and 11, while one 5S rDNA locus was successfully marked at pericentromeric region of the short arm of chromosome 09. In D_b, three 45S rDNA loci and two 5S rDNA loci were found out. Among them, two 45S rDNA loci were located at the terminal of the short arm of chromosomes D_b07 and D_b09, whilst one 5S rDNA locus was found situating near centromeric region of the short arm of chromosome D_b09. The positions of the BAC clones specific to the 13 individual chromosomes from D_h were compared between D₁, D₈ and D_b. The result showed the existence of chromosomal collinearity within D₁ and D₈, and as well between them and D_b. The results will serve as a base for understanding chromosome structure of cotton and polyploidy evolution of cotton genome and will provide bio-information for assembling the sequences of finished and the on-going cotton whole genome sequencing projects.