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We use approaches of comparative molecular biology, genomics, phylogenetics, and bioinformatics to study various major issues in the evolution of genes and genomes. Current studies fall into four areas:
Horizontal Gene Transfer in Plants - Horizontal gene transfer (HGT) is now recognized as a major evolutionary genetic force driving genomic and phenotypic change in prokaryotes and many unicellular eukaryotes. In contrast, there is little published evidence that HGT is common or important in the major groups of multicellular eukaryotes (animals, plants, and fungi). We recently discovered that HGT of mitochondrial genes in plants is both widespread and recent and have now expanded this work in several directions. Our efforts focus on plant mitochondrial genomes because their evident propensity for HGT and certain other attributes make them a model system for investigating HGT in eukaryotes. These studies assess rates, patterns, extents, chimeric consequences, directionality, donor/recipient relationships, functionality, and mechanistic aspects of HGT across many lineages of plant mitochondrial genomes. Our recent work has provided insight into mechanisms of HGT (it frequently occurs by direct physical contract between parasitic plants and their host plants) and has identified a plant whose mitochondrial genome has been radically shaped by HGT (it contains numerous genes acquired by HGT, and from a wide variety of donors, from other flowering plants to mosses).
Transfer of Mitochondrial Genes to the Nucleus - We are using flowering plants as a model "system" to study the evolutionary transfer of mitochondrial genes to nucleus. This process occurred on a massive scale early in mitochondrial evolution, and is therefore of fundamental importance to all eukaryotes, but continues to a significant extent only in plants. We have identified a number of very recent cases of gene transfer, which we are studying to elucidate underlying mechanisms and to characterize intermediates in the gene transfer process, e.g., plants which contain and express the same gene in both the organelle and the nucleus. We are also asking why some genes are transferred surprisingly frequently, hundreds of times during plant evolution, why certain lineages of plants transfer genes at highly elevated rates, and whether nuclear genes of mitochondrial origin are ever recaptured by the mitochondrial genome.
Accelerated Evolution of Mitochondrial Genes - We have discovered two separate lineages of plants whose mitochondrial genes are evolving at a highly accelerated rate, up to 4,000 times faster than in other plants. In each group, multiple major increases in the mutation rate have occurred, in some cases followed by major decreases. Current efforts seek to elucidate the molecular bases of these unprecedented changes in the fundamental mutation rate and to investigate whether such exceptionally high mutation rates have had any secondary effects on mitochondrial genome evolution and function.
Molecular Phylogeny - Although elucidating organismal phylogeny is no longer a primary goal of our research, a phylogenetic perspective necessarily informs almost all of our molecular evolutionary studies. As a consequence, valuable insights into important phylogenetic issues are often an unexpected bonus of our work. Our recent phylogenetic studies have identified what may be the earliest eukaryotes, land plants, and flowering plants, and have radically revised our concepts of seed plant evolution.