DENTON, AMY L.*, BETTY L. MCCONAUGHY, AND BENJAMIN D. HALL. Departments of Botany and Genetics, University of Washington, Seattle, WA 98195. - Land plant phylogeny estimation using RNA polymerase II sequences.
Ribosomal DNA genes are the most widely used nuclear sequences for
phylogeny reconstruction at higher taxonomic levels in plants.
However, sequence data from additional, independent nuclear loci may
be required to better understand the early diversification of basal
land plant lineages. Toward this end, we developed a set of primers
that were used to PCR-amplify and sequence a 1.7 kb region of
protein-coding DNA from RPB2, the gene encoding the
second-largest subunit of RNA polymerase II. RPB2 sequences
were obtained from over 30 green plant taxa including eudicot,
monocot, and basal angiosperm species, representatives of the four
major gymnosperm orders, and a liverwort. Green plant RPB2
sequences were aligned unambiguously and maximum parsimony and maximum
likelihood phylogenetic analyses were performed. Comparisons of
rbcL, rDNA and ,RPB2 based trees will be discussed. In
general, trees generated using RPB2 data are concordant with
those based on 18S rDNA sequences. Within gymnosperms, the cycads,
Gingko, Gnetales and Coniferales are monophyletic, and the
Pinaceae are basal to the other coniferous families. In contrast to
rbcL trees, the RPB2 data do not suggest that the
Gnetales are sister to the angiosperms. Within angiosperms, eudicots
and monocots form well-supported clades and the Austrobaileyaceae
consistently appear among the earliest branching groups. These
analyses provide evidence for the utility of RPB2 sequences in
the estimation of evolutionary relationships among land plants.
Key words: land plants, molecular phylogeny, nuclear gene, RNA polymerase II