Sequencing Chloroplast Genomes of Native and Endangered Hawaiian Plants

During a period of rapid speciation over the past 5 million years the endemic Hawaiian mints have diverged into a group of 60 species in three genera and represent a remarkable array of phenotypes. Today, many members of this group are endangered or already extinct and therefore primarily known and available only from herbarium samples collected during the last century. Phylogenetic analyses have been utilized with a gene-by-gene approach to investigate evolution in this lineage, but its recent diversification means that sequence divergence, and hence phylogenetic resolution, is low. Furthermore, incongruence exists between maternally inherited chloroplast and biparentally inherited nuclear loci, suggesting a hybrid origin for this radiation. Therefore, a genomic approach is necessary to gain a better understanding of the rapid diversification of this lineage. Unfortunately genetic resources are limited and no genome-wide analyses have been generated for close relatives of the Hawaiian mints. We used next-generation sequencing methods to obtain sequences of the chloroplast genome. Since chloroplast genomes are only available from distantly related species, several analytical methods were performed to assemble the sequence data. A nearly complete genome has been recovered from a ca. 80-year-old herbarium sample, which can be used as a reference for assembling the chloroplast genomes of other poorly known endemic Hawaiian mint species. Phylogenetic analysis of hypervariable regions will be performed to examine evolutionary relationships among and the origin of these morphologically heterogeneous plants. Such examination will help elucidate the process of rapid evolution of morphological characteristics that are related to environmental adaptation.