In situ hybridization of biotinylated DNA probes to cotton meiotic chromosomes

Establishment of a multi-color genomic in situ hybridization technique to simultaneously discriminate the three interspecific hybrid genomes in gossypium

To identify alien chromosomes in recipient progenies and to analyze genome components in polyploidy, a genomic in situ hybridization (GISH) technique that is suitable for cotton was developed using increased stringency conditions. The increased stringency conditions were a combination of the four factors in the following optimized state: 100:1 ratio of blocking DNA to probe, 60% formamide wash solution, 43 degrees C temperature wash and a 13 min wash. Under these specific conditions using gDNA from Gossypium sturtianum (C(1)C(1)) as a probe, strong hybridization signals were only observed on chromosomes from the C(1) genome in somatic cells of the hybrid F(1) (G. hirsutum x G. sturtianum) (A(t)D(t)C(1)). Therefore, GISH was able to discriminate parental chromosomes in the hybrid. Further, we developed a multi-color GISH to simultaneously discriminate the three genomes of the above hybrid. The results repeatedly displayed the three genomes, A(t), D(t), and C(1), and each set of chromosomes with a unique color, making them easy to identify. The power of the multi-color GISH was proven by analysis of the hexaploid hybrid F(1) (G. hirsutum x G. australe) (A(t)A(t)D(t)D(t)G(2)G(2)). We believe that the powerful multi-color GISH technique could be applied extensively to analyze the genome component in polyploidy and to identify alien chromosomes in the recipient progenies.

Integrative mapping of Gossypium hirsutum L. by meiotic fluorescent in situ hybridization of a tandemly repetitive sequence (B77)

We determined the relative positions of the tandem-repeat molecular cytogenetic marker B77, translocation breakpoints, and telosome arms in Gossypium hirsutum cytogenetic stocks by fluorescence in situ hybridization (FISH) analysis of meiotic quadrivalents in 16 single and 2 double translocation heterozygotes and five monotelodisomics. Results delimited the B77 FISH locus to the right arm of the D-subgenome chromosome 14 (14R) and the short arm (14sh), respectively. By equating 14R with 14sh and 14L (left) with 14Lo (long), the findings established a unified nomenclature for the arms of chromosome 14. Previously reported chromosome 14 arm locations were confirmed for four of the five translocations involving chromosome 14, namely NT1L-14L (2780), NT2R-14R (2B-1), NT14L-23R (2777), and NT14R-24R (2781), whereas the location of breakpoint T6L-14L was not confirmed and was reassigned to arm 14R. When used as a probe on Southern blots, the B77 signal was associated with a terminus of the D-subgenome RFLP linkage group (LG) D04 by linkage analysis of an interspecific F(2) population, now known to be chromosome 20. However, additional codominant DNA marker information in the affected region excluded the B77 polymorphism detected by Southern blot hybridization from chromosome 20 and, indeed, from the remainder of the genome.

Comparison of chromosome BrdU-Hoechst-Giemsa banding patterns of the A1 and (AD)2 genomes of cotton

The karyotypes of diploid cotton, Gossypium herbaceum L. var. africanum (Watt) Mauer, and tetraploid cotton, Gossypium barbadense L., were studied by BrdU-Hoechst-Giemsa banding, using a specially developed image-analysis system. The patterns obtained are represented by the slightly and intensively stained bands that correspond, respectively, to the early replicating DNA and the DNA replicating in the mid and late S period. The number of main Giemsa-positive bands varies from 2 to 9 per chromosome. The banding patterns of all homologous pairs are specific in both the A1 and (AD)2 genomes. This made possible the complete classification of the chromosomes. Based on the similarity of the BrdU-Hoechst-Giemsa banding patterns and the sizes of the chromosomes in the A1 and (AD)2 genomes, we divided the (AD)2 genome into Ab and Db subgenomes and classified their chromosomes according to the A1 genome chromosome classification. The BrdU-Hoechst-Giemsa banding pattern of the Db subgenome is basically similar to that of the A1 genome and Ab subgenome, but the differences between it and the banding patterns of the A1 genome and Ab subgenome are more significant than the differences between the latter two genomes. The similarity of the intragenomic banding patterns between nonhomologous chromosomes a and b, c and g, d and e, f and j, h and i, and l and m was revealed. Based on our results, we suggest that the ancestral cotton genome contained 7 homologous pairs of chromosomes. The results prove the feasibility of image-analysis techniques for identification and quantitative analysis of chromosomes, especially with regard to small-chromosome species.Key words: cotton, A1 and (AD)2 genomes, chromosome identification, BrdU-Hoechst-Giemsa banding, image analysis.

Use of meiotic FISH for identification of a new monosome in Gossypium hirsutum L

The extensive use of molecular cytogenetics in human genetics and clinical diagnostics indicates that analogous applications in plants are highly feasible. One sort of application would be the identification of new aneuploids, which traditionally involves either direct karyotypic identification, which is feasible in only a few plant species, or tests with markers (cytogenetic, genetic, or molecular), which require sexual hybridization and at least one subsequent seed or plant generation. We have used meiotic fluorescence in situ hybridization (FISH) to analyze a new monosome of cotton (Gossypium hirsutum L., 2n = 4x = 52, 2(AD)1) that had a phenotype which seemed to be distinct from monosomes in the Cotton Cytogenetic Collection. Painting with A2-genome DNA revealed the monosome's D-subgenome origin. DAPI-PI staining showed that the monosome carries a major NOR, delimiting it to the major NOR-bearing chromosomes of the D-subgenome, i.e., 16 or 23. Dual-color FISH with 5S and 18S-28S rDNAs indicated that the monosome contains separate major clusters of each of these two tandemly repeated rDNA elements, thus delimiting the monosome to chromosome 23, for which the Cotton Cytogenetic Collection has previously been devoid of any sort of deficiency. Of the 26 chromosomes in the cotton genome, the Collection now provides coverage for 16 (70%) in the form of monosomy, and 20 (77%) in the form of monosomy and (or) telosomy. Use of molecular cytogenetic methods to identify a new plant aneuploid in cotton exemplifies the fact that a physicochemical karyotypic chromosome identification system is not required a priori for application of new molecular cytogenetic methods, thus indicating their potential applicability to nearly all plant species.

In situ hybridization of plant meiotic and mitotic chromosomes: differences in signal detection

The technique of in situ hybridization to both meiotic and mitotic chromosomes of Rumex acetosa is described. Differences in the efficiency of signal detection were observed between the two types of material. The implications of these results for in situ hybridization to other plant species are explored.