Prospects for introgressing tomato chromosomes into the potato genome: An assessment through GISH analysis

With a view to assess the possibility of homoeologous pairing and crossing-over between the chromosomes of potato (Solanum tuberosum) and tomato (Lycopersicon esculentum), a somatic fusion hybrid and two monosomic alien tomato addition genotypes were investigated through genomic in situ hybridisation (GISH). The somatic fusion hybrid, C31-17-51, was near hexaploid (2n = 6x - 4 = 68) possessing 46 potato chromosomes + 20 tomato chromosomes + 2 translocated chromosomes. The two alien addition genotypes were near tetraploids (2n = 4x + 1 = 49) and consisted of monosomic alien additions for tomato chromosome 1 in genotype 2103-1, and tomato chromosome 8 in genotype 2301-2. In the fusion hybrid the tomato pachytene chromosome identification revealed that the chromosomes 1, 2, 5, 6, 7, 10, and 12 were in diploid condition whereas among those that were in haploid condition, three could be identified viz., 4, 9, and 11. The remaining three chromosomes could not be cytologically identified. Although the chromosomes with translocated segments could not be identified at the pachytene stage due to technical difficulties, there was clear evidence for the presence of a reciprocal translocation observed at diakinesis and metaphase I stages. Because of autosyndetic pairing of the translocated segments, it gave a false impression as if there was a high frequency (86.0%) of allosyndetic pairing. In contrast to the fusion hybrid, the two alien monosomic addition genotypes showed a very low frequency of allosyndetic pairing, namely 1.1 and 1.3% respectively for the monosomic additions 1 and 8. In the genotype 2301-2, monosomic addition for tomato chromosome 8, crossing-over between the homoeologous chromosomes was estimated to occur in 0.8% of the meiotic cells investigated. Despite this low frequency of homoeologous pairing and crossing-over, there is a possibility for introgressing tomato chromosomal DNA into the potato genome through intergenomic recombination

Prospects for introgressing tomato chromosomes into the potato genome: An assessment through GISH analysis

With a view to assess the possibility of homoeologous pairing and crossing-over between the chromosomes of potato (Solanum tuberosum) and tomato (Lycopersicon esculentum), a somatic fusion hybrid and two monosomic alien tomato addition genotypes were investigated through genomic in situ hybridisation (GISH). The somatic fusion hybrid, C31-17-51, was near hexaploid (2n = 6x - 4 = 68) possessing 46 potato chromosomes + 20 tomato chromosomes + 2 translocated chromosomes. The two alien addition genotypes were near tetraploids (2n = 4x + 1 = 49) and consisted of monosomic alien additions for tomato chromosome 1 in genotype 2103-1, and tomato chromosome 8 in genotype 2301-2. In the fusion hybrid the tomato pachytene chromosome identification revealed that the chromosomes 1, 2, 5, 6, 7, 10, and 12 were in diploid condition whereas among those that were in haploid condition, three could be identified viz., 4, 9, and 11. The remaining three chromosomes could not be cytologically identified. Although the chromosomes with translocated segments could not be identified at the pachytene stage due to technical difficulties, there was clear evidence for the presence of a reciprocal translocation observed at diakinesis and metaphase I stages. Because of autosyndetic pairing of the translocated segments, it gave a false impression as if there was a high frequency (86.0%) of allosyndetic pairing. In contrast to the fusion hybrid, the two alien monosomic addition genotypes showed a very low frequency of allosyndetic pairing, namely 1.1 and 1.3% respectively for the monosomic additions 1 and 8. In the genotype 2301-2, monosomic addition for tomato chromosome 8, crossing-over between the homoeologous chromosomes was estimated to occur in 0.8% of the meiotic cells investigated. Despite this low frequency of homoeologous pairing and crossing-over, there is a possibility for introgressing tomato chromosomal DNA into the potato genome through intergenomic recombination

Chromosome painting in plants.

The current 'state-of-art' as to chromosome painting in plants is reviewed. We define different situations described as painting so far: i) Genomic in situ hybridisation (GISH) with total genomic DNA to distinguish alien chromosomes on the basis of divergent dispersed repeats, ii) 'Chromosomal in situ suppression' (CISS) hybridisation with chromosome-derived DNA probes and blocking of interchromosomally dispersed repeats by total genomic or C0 t-1 DNA in excess, iii) exceptional cases of single chromosome painting by probes containing chromosome-specific dispersed repeats, and iv) Fluorescence in situ hybridisation (FISH) with extended contigs of large insert clones for painting of those chromosomes of a euploid complement which harbour the cloned sequences. While GISH was successfully applied in most plant hybrids and/or their derivatives, painting of individual chromosomes by CISS hybridisations of chromosome-specific DNA probes have so far not revealed convincing results in plants. The reason for this failure and the use of possible alternative approaches are discussed. At least for small plant genomes, painting by large insert single sequence clones provides a promising alternative tool to solve cytogenetic questions, which up to now could not be tackled otherwise. An example of such a painting is described in detail for Arabidopsis thaliana