A evolução pode provocar rápida redução no tamanho de genomas

sexta-feira, abril 22, 2011

Evolution can cause a rapid reduction in genome size

Despite being closely related to the lyre-leaved rock cress, the thale cress has a considerably smaller genome

April 21, 2011

It would appear reasonable to assume that two closely related plant species would have similar genetic blueprints. However, scientists from the Max Planck Institute for Developmental Biology in Tübingen, working in cooperation with an international research team have now decoded, for the first time, the entire genome of the lyre-leaved rock cress (Arabidopsis lyrata), a close relative of the thale cress (Arabidopsis thaliana), the model plant used by geneticists. They discovered that the genome of the lyre-leaved rock cress is fifty percent bigger than that of the thale cress. Moreover, these changes arose over a very short period in evolutionary terms. This new high-quality genome analysis will provide a basis for further detailed comparative studies on the function, ecology and evolution of the plant genus Arabidopsis.

Flowers of Arabidopsis lyrata (left) und Arabidopsis thaliana (right). 
© Ya-Long Guo/MPI for Developmental Biology

Genome size among the different species of the plant kingdom varies significantly. At the upper end of the currently known spectrum, scientists have identified the herb Paris or true-lover’s knot (Parisquadrifolia), whose genome is a good thousand times longer than that of the carnivorous plants from the genusGenlisea. However, these plants are so distantly related that it is almost impossible to identify the evolutionary forces at work in the individual species. Therefore, researchers from Detlef Weigel’s Department of Molecular Biology at the Max Planck Institute for Developmental Biology in Tübingen working in cooperation with an international research team selected for their genome study a species closely related to the thale cress (Arabidopsis thaliana), probably the most widely studied flowering plant in genetics. The species in question was lyre-leaved rock cress (Arabidopsis lyrata) which, unlike thale cress, is unable to self-fertilise. “Thale cress and lyre-leaved rock cress shared an ancestor around ten million years ago, after which their evolutionary lineages diverged,” explains Ya-Long Guo from the MPI for Developmental Biology.

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The Arabidopsis lyrata genome sequence and the basis of rapid genome size change

Tina T Hu, Pedro Pattyn, Erica G Bakker, Jun Cao, Jan-Fang Cheng, Richard M Clark, Noah Fahlgren, Jeffrey A Fawcett, Jane Grimwood, Heidrun Gundlach, Georg Haberer, Jesse D Hollister, Stephan Ossowski, Robert P Ottilar, Asaf A Salamov, Korbinian Schneeberger, Manuel Spannagl, Xi Wang, Liang Yang, Mikhail E Nasrallah, Joy Bergelson, James C Carrington, Brandon S Gaut, Jeremy Schmutz, Klaus F X Mayer et al.

Corresponding authors

Nature Genetics (2011) doi:10.1038/ng.807Received 13 September 2010 Accepted 18 March 2011 Published online 10 April 2011
We report the 207-Mb genome sequence of the North American Arabidopsis lyrata strain MN47 based on 8.3× dideoxy sequence coverage. We predict 32,670 genes in this outcrossing species compared to the 27,025 genes in the selfing species Arabidopsis thaliana. The much smaller 125-Mb genome of A. thaliana, which diverged from A. lyrata 10 million years ago, likely constitutes the derived state for the family. We found evidence for DNA loss from large-scale rearrangements, but most of the difference in genome size can be attributed to hundreds of thousands of small deletions, mostly in noncoding DNA and transposons. Analysis of deletions and insertions still segregating inA. thaliana indicates that the process of DNA loss is ongoing, suggesting pervasive selection for a smaller genome. The high-quality reference genome sequence for A. lyrata will be an important resource for functional, evolutionary and ecological studies in the genus Arabidopsis.