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      Analyses of Synteny Between Arabidopsis thaliana and Species in the Asteraceae Reveal a Complex Network of Small Syntenic Segments and Major Chromosomal Rearrangements

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          Abstract

          Comparative genomic studies among highly divergent species have been problematic because reduced gene similarities make orthologous gene pairs difficult to identify and because colinearity is expected to be low with greater time since divergence from the last common ancestor. Nevertheless, synteny between divergent taxa in several lineages has been detected over short chromosomal segments. We have examined the level of synteny between the model species Arabidopsis thaliana and species in the Compositae, one of the largest and most diverse plant families. While macrosyntenic patterns covering large segments of the chromosomes are not evident, significant levels of local synteny are detected at a fine scale covering segments of 1-Mb regions of A. thaliana and regions of <5 cM in lettuce and sunflower. These syntenic patches are often not colinear, however, and form a network of regions that have likely evolved by duplications followed by differential gene loss.

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          Most cited references 39

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          Polyploidy and genome evolution in plants.

          Genome doubling (polyploidy) has been and continues to be a pervasive force in plant evolution. Modern plant genomes harbor evidence of multiple rounds of past polyploidization events, often followed by massive silencing and elimination of duplicated genes. Recent studies have refined our inferences of the number and timing of polyploidy events and the impact of these events on genome structure. Many polyploids experience extensive and rapid genomic alterations, some arising with the onset of polyploidy. Survivorship of duplicated genes are differential across gene classes, with some duplicate genes more prone to retention than others. Recent theory is now supported by evidence showing that genes that are retained in duplicate typically diversify in function or undergo subfunctionalization. Polyploidy has extensive effects on gene expression, with gene silencing accompanying polyploid formation and continuing over evolutionary time.
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            Functional divergence of duplicated genes formed by polyploidy during Arabidopsis evolution.

            To study the evolutionary effects of polyploidy on plant gene functions, we analyzed functional genomics data for a large number of duplicated gene pairs formed by ancient polyploidy events in Arabidopsis thaliana. Genes retained in duplicate are not distributed evenly among Gene Ontology or Munich Information Center for Protein Sequences functional categories, which indicates a nonrandom process of gene loss. Genes involved in signal transduction and transcription have been preferentially retained, and those involved in DNA repair have been preferentially lost. Although the two members of each gene pair must originally have had identical transcription profiles, less than half of the pairs formed by the most recent polyploidy event still retain significantly correlated profiles. We identified several cases where groups of duplicated gene pairs have diverged in concert, forming two parallel networks, each containing one member of each gene pair. In these cases, the expression of each gene is strongly correlated with the other nonhomologous genes in its network but poorly correlated with its paralog in the other network. We also find that the rate of protein sequence evolution has been significantly asymmetric in >20% of duplicate pairs. Together, these results suggest that functional diversification of the surviving duplicated genes is a major feature of the long-term evolution of polyploids.
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              The origins of genomic duplications in Arabidopsis.

              Large segmental duplications cover much of the Arabidopsis thaliana genome. Little is known about their origins. We show that they are primarily due to at least four different large-scale duplication events that occurred 100 to 200 million years ago, a formative period in the diversification of the angiosperms. A better understanding of the complex structural history of angiosperm genomes is necessary to make full use of Arabidopsis as a genetic model for other plant species.
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                Author and article information

                Journal
                Genetics
                Genetics
                Genetics Society of America
                0016-6731
                1943-2631
                August 23 2006
                August 2006
                August 2006
                June 18 2006
                : 173
                : 4
                : 2227-2235
                Article
                10.1534/genetics.105.049205
                1569713
                16783026
                089b838e-f789-4e83-bd55-dd49b2a93002
                © 2006

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