Comparative analyses of land plant plastid genomes
The availability of complete plastid genomes has been playing an important role in resolving phylogenetic relationships among the major clades of land plants and in improving our understanding of the evolution of genomic organization. The increased availability of complete genome sequences has enabled researchers to build large multi-gene datasets for phylogenetic and molecular evolutionary studies. In chapter 2 of this thesis a web-based multiple sequence web viewer and alignment tool (MSWAT) is developed to handle large amount of data generated from complete genome sequences for phylogenetic and evolutionary analyses. We expect that MSWAT will be of general interest to biologists who are building large data matrices for evolutionary analyses. The third chapter presents the sequenced plastid genomes of three magnoliids, Drimys (Canellales), Liriodendron (Magnoliales), and Piper (Piperales). Data from these genomes, in combination with 32 other angiosperm plastid genomes, were used to assess phylogenetic relationships of magnoliids to other angiosperms and to examine patterns of variation of GC content. Evolutionary comparisons of three new magnoliid plastid genome sequences, combined with other published angiosperm genomes, confirm that GC content is unevenly distributed across the genome by location, codon position, and functional group. Furthermore, phylogenetic analyses provide the strongest support so far for the hypothesis that the magnoliids are sister to a large clade that includes both monocots and eudicots. The fourth chapter presents the Trifolium subterraneum plastid genome sequence, which is unusual in genome size and organization relative to other angiosperm plastid genomes. The Trifolium plastid genome is an excellent model system to examine mechanisms of rearrangements and the evolution of repeats and unique DNA.