Location: National Clonal Germplasm RepositoryTitle: Insights into phylogeny, sex function and age of Fragaria based on whole chloroplast genome sequencing Author
Submitted to: Molecular Phylogenetics and Evolution
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 8/30/2012
Publication Date: 9/13/2012
Citation: Njuguna, W., Liston, A., Cronn, R., Ashman, T., Bassil, N.V. 2012. Insights into phylogeny, sex function and age of Fragaria based on whole chloroplast genome sequencing. Molecular Phylogenetics and Evolution. http://dx.doi.org/10.1016/j.bbr.2011.03.031. Interpretive Summary: The cultivated strawberry is one of the youngest domesticated plants, developed in France in the 1700s from chance hybridization between two western hemisphere strawberries. However, little is known about the evolution of strawberry plants that gave rise to this important fruit crop. We examined maternally inherited DNA from 21 strawberry types or species. We found out that the western North American diploid (with only two sets of chromosomes as compared with the eight present in the domestic strawberry cultivars) strawberry is the likely mother to the domestic strawberry and its immediate ancestors. Two groups of this North American diploid type were identified. A Pacific Coast group was found in British Columbia, Oregon and California while the other group was distributed in Idaho and Colorado. The Pacific Coast group appears to have contributed as both the maternal lineage and a source of male-sterility in strawberries. We also found evidence that the loss of male and female function can follow increase in numbers of chromosomes. Strawberry has apparently attained its current distribution at comparable latitudes across the equator but not in the tropics in the past 1.72 million years. The strawberry group containing the domestic strawberry ancestors is estimated to be younger than expected, at less than 573,000 years old.
Technical Abstract: The cultivated strawberry is one of the youngest domesticated plants, developed in France in the 1700s from chance hybridization between two western hemisphere octoploid species. However, little is known about the evolution of the species that gave rise to this important fruit crop. Phylogenetic analysis of chloroplast genome sequences of 21 Fragaria species and subspecies resolves the western North American diploid F. vesca ssp. bracteata as sister to the clade of octoploid/decaploid species. No extant tetraploids or hexaploids are directly involved in the ancestry of the octoploids. There is strong geographic segregation of chloroplast haplotypes in subsp. bracteata, and the gynodioecious Pacific Coast populations are implicated as both the maternal lineage and the source of male-sterility in the octoploid strawberries. Analysis of sexual system evolution in Fragaria provides evidence that the loss of male and female function can follow polyploidization, but does not seem to be associated with loss of self-incompatibility following genome doubling . Based on character-state mapping analysis, the evolution of two reproductive traits, mating and sexual system, within Fragaria is discussed. Fragaria has apparently attained its circumboreal and amphitropical distribution in the past 1.72 million years, and the octoploid clade is estimated to be less than 573,000 years old.