Submitted to: Genome
Publication Type: Peer reviewed journal
Publication Acceptance Date: 1/20/2008
Publication Date: 5/5/2008
Citation: Pendinen, G., Gavrilenko, T., Jiang, J., Spooner, D.M. 2008. Allopolyploid speciation of the Mexican tetraploid potato species Solanum stoloniferum and S. hjertingii revealed by genomic in situ hybridization. Genome. 51(9):714-720(7). Interpretive Summary: The common potato of world commerce, Solanum tuberosum, has a rich genepool of about 190 wild and cultivated species that are of great importance to potato breeders because they can be used as breeding stock to improve the tastes, productivity, or disease resistance of the cultivated potato. There is great variation in the number of chromosomes in wild potatoes, with about 70% of the species having 24 chromosomes (technically called diploids), and the rest (polyploids) having higher numbers of 36 (triploids), 48 (tetraploids), 60 (pentaploids, and 72 (hexaploids). Some of these polyploids are thought to have been formed by the crossing of two different diploid (or diploid and tetraploid) species, and for the polyploids to maintain a mixture of the genes and chromosomes of both of their parents. This study examined this idea by examining the chromosomes of two of the tetraploid species, Solanum hjertingii and S. stoloniferum, grouped scientifically in the “Longipedicellata series.” By a technique called “chromosome painting” we are able to show that these two species have origins from two separate groups of species from Mexico. These results provide the first insights into evolution of the polyploid members of sect. Petota through this technique.
Technical Abstract: About 20% of the wild potato (Solanum sect. Petota) species are polyploid, with 15% of them tetraploid at 2n = 4x = 48. Determination of the type of polyploidy and the development of the genome concept for members of sect. Petota has been based mainly on the analysis of chromosome pairing in species and their hybrids. Although there are minor differences among authors, most agree that the wild tetraploid species in ser. Longipedicellata have a genome designation AABB. We investigated this hypothesis with fluorescent in situ hybridization (GISH and FISH) in ser. Longipedicellata members S. stoloniferum S. hjertingii, based on prior hypotheses and recent data from DNA sequencing phylogenies. Our results support an AABB genome constitution for these species with the diploid species S. verrucosum (A genome) and unspecified B genome species to possibly include the remaining Mexican diploid species such as S. cardiophyllum, S. jamesii, or S. ehrenbergii (PI 275216), or their recent progenitors. In addition, all of these investigated diploid species have one terminally located 45S rDNA locus on the one chromosome pair and one 5S rDNA locus on another chromosome pair. S. stoloniferum has two chromosome pairs with one 45S rDNA locus and two another pairs of chromosomes with the 5S rDNA locus. Similar to the diploid species, the 5S rDNA locus of S. stoloniferum showed a relatively small size compared to the 45S locus. The two pairs of the 45S rDNA-bearing chromosomes of S. stoloniferum have different sizes of the 45S rDNA regions. In the sequential GISH and FISH experiments it was shown that one pare of chromosomes of the B subgenome of S. stoloniferum has the large 45S rDNA region. Whereas one pare of the A subgenome of S. stoloniferum has the small 45S rDNA regions. It is possible that the 45S rDNA regions of two subgenomes of S. stoloniferum were changed during coevolution of A and B genomes of this allotetraploid species.