SHERWOOD, ANNA M1*, PAMELA S SOLTIS2, and DOUGLAS E SOLTIS3. 1School of Biological Science, Washington State University, Pullman WA, 99164-4236; 2Florida Museum of Natural History and the Genetics Institute, University of Florida, Gainesville, FL 32611; 3Department of Botany and the Genetics Institute, University of Florida, Gainesville, FL 32611. - ITS sequence variation in Tragopogon (Asteraceae): phylogeny and gene evolution in allopolyploids.
Over half of all plant species are derived through polyploidy.
However, despite the prevalence of polyploid speciation little is
known about the genetic consequences of polyploidy. Three diploid
species of Tragopogon were introduced from Europe to the
Palouse region of eastern Washington and adjacent Idaho in the early
1900s. These species hybridized, and two allotetraploid species were
formed: T. mirus and T. miscellus. The parentage of
these tetraploid species is well documented, and the tetraploids are
serving as models for the study of various aspects of polyploid
evolution. We have reconstructed the phylogeny of Tragopogon, a
largely Eurasian genus of about 50 species, using sequences of the
internal transcribed spacers (ITS) of the nuclear ribosomal DNA. Our
results suggest that the three diploid progenitor species of the
Palouse tetraploids are distantly related. We also used DNA sequence
variation in the ITS regions of T. mirus, T. miscellus,
and their diploid parents to determine whether or not concerted
evolution had homogenized the rDNA arrays in the tetraploids during
the approximately 70-80 years since their formation. Two populations
of each allotetraploid and its diploid parents were sampled, and each
population was represented by three or more individuals, with four or
more clones per individual. The ITS sequences of the diploid parents
of T. mirus differed at 18 nucleotide positions; those of the
parental species of T. miscellus differed at 16 sites. Cloned
PCR products from each tetraploid match the sequence of the respective
parents. These results indicate that the rDNA arrays of the recent
tetraploids T. mirus and T. miscellus do not appear to
have undergone concerted evolution.
Key words: Asteraceae, ITS, phylogeny, polyploidy, Tragopogon