GRAHAM, SEAN W1*, HARDEEP S RAI1, PATRICK A REEVES2, MARC A MCPHERSON1, and RICHARD G OLMSTEAD2. 1Department of Biological Sciences, University of Alberta, Edmonton, Alberta, Canada, T6G 2E9; 2Department of Botany, University of Washington, Seattle, Washington, USA 98195. - Addressing deep and difficult problems in plant molecular systematics using large-scale sequencing of the plastid genome.
Since their introduction two years ago, a series of universal primers
designed to amplify and sequence large regions of the plastid genome
-- approximately 10% of the ca. 150 kb land-plant plastome spanning,
around 17 genes -- have been used to generate large volumes of high
quality (very slowly evolving) characters across a broad range of seed
plants. This relatively inexpensive and rapid approach is
complementary to traditional "few-gene, multi taxon" and
ongoing "whole genome" approaches. The primers have been
used to produce phylogenies of a broad range of early and recent
branches of plant evolution, many aspects of which have eluded robust
phylogenetic resolution using conventional approaches. The
"universality" of the primers has now been demonstrated
across a broad range of vascular plant taxa. We provide an overview of
published and upcoming work using this approach that addresses
higher-order relationships at a variety of levels in the seed-plants,
basal angiosperms and monocots. A number of incidental structural
markers (small indels, intron losses and ORF expansion events) in the
regions examined are shown to act as additional conservative markers
of phylogeny. We also discuss how this diverse sampling of coding and
noncoding regions provides substantial leverage to examine the
molecular evolution of the plastid genome across a diverse range of
seed plants.
Key words: angiosperms, deep phylogeny, monocotyledons, spermatophytes, Universal primers