Submitted to: The Plant Genome
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 9/1/2007
Publication Date: 2/22/2008
Citation: Spooner, D.M., Rodriquez, F., Polgar, Z., Ballard, H., Jansky, S.H. 2008. Genomic origins of potato polyploids: GBSSI gene sequencing data. The Plant Genome. 48(S1):27-36. 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 looking at one gene in different polyploid species and comparing it to the diploids. In some cases, two copies of the gene are indeed maintained, and in other cases not. These results are compared to prior ideas of the parents of the polyploids; in some cases prior ideas are supported and in other cases different parents are discovered than has ever been imagined before. These results provide the first insights into evolution of the polyploid members of sect. Petota through this technique.
Technical Abstract: The common potato of world commerce, Solanum tuberosum, has a rich genepool of about 190 wild and cultivated species (Solanum section Petota) that are of great importance in potato improvement. About 70% of the wild potato species are diploid at 2n = 2x = 24, and the rest form a polyploid series of triploids, tetraploids (including the major cultivars of S. tuberosum), pentaploids, and hexaploids. Within section Petota and the closest non-tuber-bearing relatives, chromosome pairing relationships have been interpreted by genome formulae, developed through classic meiotic analysis of interspecific hybrids developed in the 1930's. Most authors agree on a five genome hypothesis (A, B, C, D, and E; with superscripted variants of these major genomes), but the identity of these genomes in the polyploids relative to the diploids has long been the subject of debate and is unresolved. The present study provides the first analysis of genome constitution of polyploids in cultivated and wild potatoes through a phylogenetic analysis of DNA sequences of a cloned low-copy nuclear gene (GBSSI or waxy). Prior chloroplast DNA analysis and waxy analysis support four (chloroplast) or three (waxy) clades in sect. Petota. GBSSI sequence analyses support some prior genome hypotheses but support others never proposed before. Novel origins are supported for the hexaploids of series Demissa (except S. demissum) to constitute members of chloroplast clades 3 (South American series Piurana) + 4 (other South American diploids), and for hexaploid S. demissum to have origins entirely within clade 4. Supporting prior hypotheses are origins of tetraploid series Longipedicellata from clades 1 (Mexican diploids) or 2 (S. bulbocastanum, S. cardiophyllum) + 4, and members of all other series (including S. demissum, ser. Acaulia, S. tuberosum), entirely from within clade 4. These results provide the first molecular insights into evolution of the polyploid members of sect. Petota.