MITOTIC INSTABILITY IN RESYNTHESIZED AND NATURAL POLYPLOIDS OF THE GENUS ARABIDOPSIS (BRASSICACEAE)

Allopolyploids contain complete sets of chromosomes from two or more different progenitor species. Because allopolyploid hybridization can lead to speciation, allopolyploidy is an important mechanism in evolution, Meiotic instability in early-generation allopolyploids contributes to high lethality, but less is known about mitotic fidelity in allopolyploids. We compared mitotic stability in resynthesized Arabidopsis suecica-like neoallopolyploids with that in 13 natural lines of A. suecica (2n = 4x = 26). We used fluorescent in situ hybridization to distinguish the chromosomal contribution of each progenitor, A. thaliana (2n = 2x =10) and A. arenosa (2n = 4x = 32). Surprisingly, cells of the paternal parent A. arenosa had substantial aneuploidy, while cells of the maternal parent A, thaliana were more stable. Both natural and resynthesized allopolyploids had low to intermediate levels of aneuploidy. Our data suggest that polyploidy in Arabidopsis is correlated with aneuploidy, but varies in frequency by species. The chromosomal composition in aneuploid cells within individuals was variable, suggesting somatic mosaicisms of cell lineages, rather than the formation of distinct, stable cytotypes. Our results suggest that somatic aneuploidy can be tolerated in Arabidopsis polyploids, but there is no evidence that this type of aneuploidy leads to stable novel cytotypes.