Rapid chromosome evolution in recently formed polyploids in Tragopogon (Asteraceae)

Area of Science:

• Evolutionary Biology
• Genetics
• Genomics

Background:

• Polyploidy, or whole genome duplication, is a significant evolutionary mechanism in eukaryotes, particularly in angiosperms.
• While the importance of polyploidy is recognized, the role of chromosome divergence in the establishment of young polyploid populations remains largely unexplored.
• This study focuses on recent allotetraploids, Tragopogon mirus and T. miscellus, to investigate chromosomal diversity.

Purpose of the Study:

• To assess the role of aberrant meiosis in generating chromosomal and genomic diversity in young polyploid populations.
• To understand the mechanisms contributing to the formation, establishment, and survival of polyploid species.
• To investigate karyotypic variation in both natural and synthetic polyploid lines.

Main Methods:

• Utilized fluorescence in situ hybridization (FISH) on natural populations of Tragopogon mirus and T. miscellus.
• Analyzed synthetic polyploid lines (S(0) and S(1) generations).
• Examined chromosomal rearrangements, polymorphism, aneuploidy, intergenomic translocations, and ribosomal DNA (rDNA) locus variations.

Main Results:

• Detected extensive chromosomal polymorphism, including aneuploidy (monosomy, trisomy), intergenomic translocations, and variable rDNA loci in natural populations.
• Observed significant karyotypic variation even among sibling plants.
• Confirmed translocations, chromosome loss, and meiotic irregularities like quadrivalent formation in synthetic polyploid lines, indicating rapid chromosomal changes post-polyploidization.

Conclusions:

• Chromosomal rearrangements and changes are common and occur rapidly following polyploidization in young polyploid species.
• Studying karyotypes of young (<150 years old) natural polyploids and comparable synthetic polyploids is crucial for understanding their evolution.
• These findings provide insights into mechanisms perturbing inheritance patterns in synthetic and young natural polyploid populations.