Altered Patterns of Fractionation and Exon Deletions in Brassica rapa Support a Two-Step Model of Paleohexaploidy

文献类型： 外文期刊

第一作者： Tang, Haibao

作者： Tang, Haibao;Tang, Haibao;Woodhouse, Margaret R.;Schnable, James C.;Pedersen, Brent S.;Freeling, Michael;Cheng, Feng;Wang, Xiaowu;Conant, Gavin;Conant, Gavin;Pires, J. Chris;Pires, J. Chris

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期刊名称：GENETICS （ 影响因子：4.562； 五年影响因子：4.845 ）

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收录情况： SCI

摘要： The genome sequence of the paleohexaploid Brassica rapa shows that fractionation is biased among the three subgenomes and that the least fractionated subgenome has approximately twice as many orthologs as its close (and relatively unduplicated) relative Arabidopsis than had either of the other two subgenomes. One evolutionary scenario is that the two subgenomes with heavy gene losses (I and II) were in the same nucleus for a longer period of time than the third subgenome (III) with the fewest gene losses. This "two-step" hypothesis is essentially the same as that proposed previously for the eudicot paleohexaploidy; however, the more recent nature of the B. rapa paleohexaploidy makes this model more testable. We found that subgenome II suffered recent small deletions within exons more frequently than subgenome I, as would be expected if the genes in subgenome I had already been near maximally fractionated before subgenome III was introduced. We observed that some sequences, before these deletions, were flanked by short direct repeats, a unique signature of intrachromosomal illegitimate recombination. We also found, through simulations, that short-single or two-gene-deletions appear to dominate the fractionation patterns in B. rapa. We conclude that the observed patterns of the triplicated regions in the Brassica genome are best explained by a two-step fractionation model. The triplication and subsequent mode of fractionation could influence the potential to generate morphological diversity-a hallmark of the Brassica genus.

分类号： R394

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