allopolyploidy

Koh J, Soltis PS & Soltis DE 2010 Homeolog loss and expression changes in natural populations of the recently and repeatedly formed allotetraploid Tragopogon mirus (Asteraceae). BMC Genomics 11:97.

  • many polyploid species have formed repeatedly
  • patterns of genome evolution and gene expression are largely unknown for natural polyploid populations of independent origin
  • we therefore examined patterns of loss and expression in duplicate gene pairs (homeologs) in multiple individuals from seven natural populations of independent origin of Tragopogon mirus (Asteraceae)
  • an allopolyploid that formed repeatedly within the last 80 years from the diploids T. dubius and T. porrifolius
  • plants representing multiple populations of this young natural allopolyploid have experienced frequent and preferential elimination of homeologous loci
  • comparable analyses of synthetic F1 hybrids showed only additivity
  • loss of homeologs and changes in gene expression are not the immediate result of hybridization, but are processes that occur following polyploidization, occurring during the early (<40) generations of the young polyploid
  • further studies are required to assess whether the results for the 30 genes so far examined are representative of the entire genome
  • six natural allopolyploids are known to have formed within the past 150 years, thus affording the opportunity to examine the nearly immediate consequences of polyploidization in nature
  • in Senecio, hybridization of diploid S. squalidus with tetraploid S. vulgaris forms a sterile triploid, S. × baxteri
  • subsequent genome duplication produced the allohexaploid S. cambrensis
  • the synthetic hybrid S. × baxteri showed immediate transcriptional changes compared to the parental expression patterns
  • this "transcriptional shock" was "subsequently calmed" in allohexaploid S. cambrensis
  • suggesting that hybridization and polyploidization have distinct effects on large-scale gene expression in this system
  • T. miscellus has formed recurrently, possibly as many as 21 times, including reciprocal formation
  • T. mirus has formed repeatedly perhaps 13 times (but not reciprocally)