A poliploidia e a mudança genômica podem resultar em mudança evolutiva?

When You've Doubled Your Genes, What's One Chromosome More Or Less? How Polyploidy And Genomic Change Can Lead To Evolutionary Change

ScienceDaily (Sep. 15, 2009) — An individual with Down syndrome and a male calico cat have one thing in common—each has an extra chromosome. For animals, most instances of an extra chromosome result in birth defects or even death, but plants are another matter entirely. Many plants are able to survive the presence of an extra copy of their entire genome (known as polyploidy) and are often even more vigorous as a result. For plants, the process of polyploidy often results in a new species, making it an important mechanism in evolution. In fact, over 80% of plants may be a product of polyploidy.

However, this extra set of chromosomes can sometimes cause confusion during meiosis, the process by which sets of chromosomes are divided up to produce egg and sperm cells, with half the number of chromosomes present in a mature plant. Many recent studies have examined the effects of polyploidy on meiosis. A recent study by Drs. Andreas Madlung, Kirsten Wright, and J. Chris Pires, published in the September issue of the American Journal of Botany, examines the effects of polyploidy on a more common type of cell division, mitosis—the process of cell division that results in daughter cells that are identical to the parent cell—which allows the plant to grow and develop.

"We had been working on genomic responses to allopolyploidy for many years in newly formed allopolyploids and had noticed some instabilities during meiosis and gamete formation in newly formed allopolyploids," Madlung said. "The commonly held belief is that in established allopolyploids, incompatibilities of the two parental genomes somehow are reconciled during the evolution of the allopolyploid species but there is only relatively little data in the literature that supports this notion.
"Our work shows that even established polyploids can harbor considerable genomic instabilities, but interestingly this is not always the case either, as the different responses in different sibling lines show."
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Genetics

Mitotic instability in resynthesized and natural polyploids of the genus Arabidopsis (Brassicaceae)1

Kirsten M. Wright2, J. Chris Pires3 and Andreas Madlung2,4
2 Department of Biology, University of Puget Sound, Tacoma, Washington 98416 USA 3 Division of Biological Sciences, University of Missouri, Columbia, Missouri 65211-7310 USA

ABSTRACT

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.

Key Words: allopolyploid • allopolyploidization • aneuploid • Arabidopsis suecica • Arabidopsis arenosa • Brassicaceae • FISH • fluorescent in situ hybridization • hybrid • mitotic instability • mitosis

Received for publication 7 August 2008. Accepted for publication 27 April 2009.

FOOTNOTES

1 The authors thank M. Morrison and S. Bennett for technical and logistical help with the plant growth facilities; L. Comai, J. Birchler, R. Martienssen, and the entire Polyploidy Consortium for stimulating discussions; and M. R. Lamb for careful reading of an earlier version of the manuscript. They also thank two anonymous reviewers for comments that significantly improved the manuscript, and M. Jost for help with figures. This study was supported by NSF Plant Genome grant DBI-0501712 to J.C.P. and A.M., NSF Major Research Instrumentation grant MRI-0619009 to A.M., and funds from the University of Puget Sound Enrichment Committee to K.M.W. and A.M.

4 Author for correspondence (amadlung@ups.edu)

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