Chromosomal locus rearrangements are a rapid response to formation of the allotetraploid Arabidopsis suecica genome

Abstract

Allopolyploidy is a significant evolutionary process, resulting in new species with diploid or greater chromosome complements derived from two or more progenitor species. We examined the chromosomal consequences of genomic merger in Arabidopsis suecica, the allotetraploid hybrid of Arabidopsis thaliana and Arabidopsis arenosa. Fluorescence in situ hybridization with centromere, nucleolus organizer region (NOR), and 5S rRNA gene probes reveals the expected numbers of progenitor chromosomes in natural A. suecica, but one pair of A. thaliana NORs and one pair of A. arenosa-derived 5S gene loci are missing. Similarly, in newly formed synthetic A. suecica-like allotetraploids, pairs of A. thaliana NORs are gained de novo, lost, and͞or transposed to A. arenosa chromosomes, with genotypic differences apparent between F 3 siblings of the same F2 parent and between independent lines. Likewise, pairs of A. arenosa 5S genes are lost and novel linkages between 5S loci and NORs arise in synthetic allotetraploids. By contrast, the expected numbers of A. arenosa-derived NORs and A. thaliana-derived 5S loci are found in both natural and synthetic A. suecica. Collectively, these observations suggest that some, but not all, loci are unstable in newly formed A. suecica allotetraploids and can participate in a variety of alternative rearrangements, some of which resemble chromosomal changes found in nature.plant ͉ polyploidy ͉ speciation ͉ translocation

Analysis of Active Nucleolus Organizing Regions in Polyploid Prairie Cordgrass (<i>Spartina pectinata</i> Link) by Silver Staining

“…Thus, the loss of nucleolar activity of the NOR observed in the 103-6x population may be a result of rapid changes in chromosomal structures and gene expressions which may be due to the formation and establishment of neopolyploidy in mixed ploidy populations co-occurring with tetraploids. This similar result has been observed in allotetraploid Arabidopsis suecica, reporting that some loci in newely formed ploidy are unstable to cause loss, gain, and rearrangement of NOR sites (Pontes et al 2004). Silver-stained NORs on mitotic chromosomes are therefore useful in determining the stabilization of newly formed polyploidy of prairie cordgrass.…”

The BOY NAMED SUE Quantitative Trait Locus Confers Increased Meiotic Stability to an Adapted Natural Allopolyploid of Arabidopsis

“…Evidence in support of this hypothesis is not found in all tested systems (see Introduction). Previous reports used FISH to determine the location and number of nucleolus-organizer region (NOR) and 5S gene clusters in A. suecica and demonstrated the loss of a pair of NORs and 5S gene clusters in A. suecica compared with its presumed ancestors (Pontes et al, 2004). The authors hypothesize that the loss of the NOR can be explained by a doublestranded break, removing the NOR-containing tip of the A. thaliana chromosome 2.…”

Mechanisms of genomic rearrangements and gene expression changes in plant polyploids

“…(42,44) However, meiotic abnormalities can be as high as 36%, which correlates with pollen sterility and low seed set in synthetic Arabidopsis allotetraploids (61) and rapid rearrangements in some specific genomic regions such as rDNA loci. (62) The various levels of genomic changes observed among different allotetraploids may be due to selection for the surviving allotetraploid individuals that can overcome meiotic abnormalities and reproductive barriers.…”