Publication details

How diploidization turned a tetraploid into a pseudotriploid

Authors

MANDÁKOVÁ Terezie GLOSS Andrew D. WHITEMAN Noah K. LYSÁK Martin

Year of publication 2016
Type Article in Periodical
Magazine / Source American Journal of Botany
MU Faculty or unit

Central European Institute of Technology

Citation
Web http://www.amjbot.org/content/103/7/1187
Doi http://dx.doi.org/10.3732/ajb.1500452
Field Genetics and molecular biology
Keywords Brassicaceae; centromere loss; chromosome fusion; chromosome translocation; diploidization; dysploidy; karyotype evolution; polyploidy; whole-genome duplication
Description PREMISE OF THE STUDY: Despite being highly fertile and occupying a large geographic region, the North American heartleaf bittercress (Cardamine cordifolia; Brassicaceae) has a puzzling triploid- like chromosome number (2n = 3x = 24). As most triploids are sterile, we embarked on a detailed analysis of the C. cordifolia genome to elucidate its origin and structure. METHODS: Mitotic and meiotic chromosome complement of C. cordifolia was analyzed by comparative chromosome painting using chromosome-specific BAC contigs of Arabidopsis thaliana. Resulting chromosome patterns were documented by multicolor fluorescence microscopy and compared with known ancestral and extant Brassicaceae genomes. KEY RESULTS: We discovered that C. cordifolia is not a triploid hybrid but a diploidized tetraploid with the prevalence of regular, diploid-like meiotic pairing. The ancestral tetraploid chromosome number (2n = 32) was reduced to a triploid- like number (2n = 24) through four terminal chromosome translocations. CONCLUSIONS: The structure of the pseudotriploid C. cordifolia genome results from a stepwise diploidization process after whole-genome duplication. We showed that translocation-based descending dysploidy (from n = 16 to n = 12) was mediated by the formation of five new chromosomes. The genome of C. cordifolia represents the diploidization process in statu nascendi and provides valuable insights into mechanisms of postpolyploidy rediploidization in land plants. Our data further suggest that chromosome number alone does not need to be a reliable proxy of species' evolutionary past and that the same chromosome number may originate either by polyploidization (hybridization) or due to descending dysploidy.
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