Tragopogon miscellus

Abstract: Tragopogon mirus Ownbey and T. miscellus Ownbey are allopolyploids that formed repeatedly during the past 80 years following the introduction of three diploids (T. dubius Scop., T. pratensis L. and T. porrifolius L.) from Europe to western North America. These polyploid species of known parentage are useful for studying the consequences of recent and recurrent polyploidization. We summarize recent analyses of the cytogenetic, genomic and genetic consequences of polyploidy in Tragopogon. Analyses of rDNA ITS (internal transcribed spacer) + ETS (external transcribed spacer) sequence data indicate that the parental diploids are phylogenetically well separated within Tragopogon (a genus of perhaps 150 species), in agreement with isozymic and cpDNA data. Using Southern blot and cloning experiments on tissue from early herbarium collections of T. mirus and T. miscellus (from 1949) to represent the rDNA repeat condition closer to the time of polyploidization than samples collected today, we have demonstrated concerted evolution of rDNA. Concerted evolution is ongoing, but has not proceeded to completion in any polyploid population examined; rDNA repeats of the diploid T. dubius are typically lost or converted in both allopolyploids, including populations of independent origin. Molecular cytogenetic studies employing rDNA probes, as well as centromeric and subtelomeric repeats isolated from Tragopogon, distinguished all chromosomes among the diploid progenitors (2n = 12). The diploid chromosome complements are additive in both allopolyploids (2n = 24); there is no evidence of major chromosomal rearrangements in populations of either T. mirus or T. miscellus. cDNA-AFLP display revealed differences in gene expression between T. miscellus and its diploid parents, as well as between populations of T. miscellus of reciprocal origin. Approximately 5% of the genes examined in the allopolyploid populations have been silenced, and an additional 4% exhibit novel gene expression relative to their diploid parents. Some of the differences in gene expression represent maternal or paternal effects. Multiple origins of a polyploid species not only affect patterns of genetic variation in natural populations, but also contribute to differential patterns of gene expression and may therefore play a major role in the long-term evolution of polyploids. © 2004 The Linnean Society of London, Biological Journal of the Linnean Society, 2004, 82, 485–501.

Abstract: Most studies of the evolution of polyploid plant species have emphasized phylogenetic issues, for example, identification of diploid progenitors and clarification of polyploid complexes. They have largely utilized evidence from comparative morphology, karyotypes and cytogenetic analysis of interploidal hybrids, as well as biochemical profiles of certain classes of compounds such as flavonoids and seed proteins. Although these studies helped greatly to elucidate the mode of origin and ancestry of many polyploid species, they were not concerned with explaining one of the most intriguing features of polyploidy which is that, in many plant genera, the polyploids are more widely distributed over more habitats than their diploid progenitors. This is a problem of the first rank because at least one-third of the Angiosperms and a higher proportion of the ferns are polyploid. Several recent hypotheses have proposed that the wide capabilities of allopolyploids (we use allotetraploids as an example) are a direct biochemical consequence of their possession of two divergent diploid genomes which provides them with a multiplicity of enzymes relative to both diploid parents as well as a high proportion of novel enzymes (Fincham, 1969; Barber, 1970; Manwell and Baker, 1970). Enzyme multiplicity may extend the range of environments in which normal development can take place and, thereby, might account for the frequently wider distribution of polyploids. This may be true even if the tetraploid as a species is less poly-