Phylogenetics and Plastid Genome Evolution of Vanilloideae (Orchidaceae)

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A grant has been awarded to Dr. Kenneth M. Cameron at The New York Botanical Garden to continue his laboratory and field studies on the evolution and classification of the orchid subfamily Vanilloideae, which includes Vanilla planifolia -- the only orchid species out of approximately 25,000 that has significant agricultural value. These are considered an ancient lineage of relatively primitive orchids that are found worldwide in distribution. They have always been considered critical to fully understanding the evolution and classification of the large orchid family, but have resisted attempts to shoehorn them into traditional subfamilies. Previous molecular research by Dr. Cameron has shown these vanilloid orchids to represent a separate, distinct subfamily that is the most primitive of all but two genera of orchids. However, the relationships of the species within the subfamily are still unclear. These findings emphasize the evolutionarily pivotal position occupied by these plants and the need for further, in-depth systematic investigation. Specifically, the research will include a molecular component that will focus on constructing a solid evolutionary tree for the subfamily using DNA sequences from a suite of nuclear, chloroplast, and mitochondrial genes. However, the molecular aspect of the project will not be limited to DNA sequencing. In addition, select genes and their products from within the chloroplast genome will be studied in detail to better understand the pattern and process of degeneration of the photosynthetic apparatus among the non-green taxa that live as parasites on soil fungi. Already, Dr. Cameron has investigated three different classes of photosynthesis genes, and has discovered that two of the three (rbcL and psaB, but not atpB) are characterized by significant deletions in some of the non-photosynthetic taxa, and extremely high rates of mutation in others. These findings suggest that the vanilloid orchids are in the early stages of chloroplast genome degradation. They are, therefore, an ideal group of organisms in which to study this biological phenomenon. Finally, in addition to molecular research, new studies on floral morphology and pollination biology in the group will be initiated. Many of the vanilloid taxa are characterized by complex flowers with prominent petal ornamentation in the form of mobile scales and bristles. These structures, in particular, are unlike any other in the orchid family. They deserve careful examination in order to understand their form, function, and evolutionary derivation. The vanilloid orchids have been long recognized as an economically valuable and unique group of plants, but several aspects of their natural history have been the source of controversy among biologists. A more thorough knowledge of this pivotal group undoubtedly will be valuable to our understanding of the evolution and diversity within the second largest family of flowering plants on Earth. Despite the economic importance of Vanilla to humankind, there exist few thorough systematic investigations of these plants. Comparative morphological, anatomical, and pollination studies of the group are also lacking. For these reasons, the combined results of these morphological and molecular studies should provide a solid phylogeny of Vanilloideae for which nomenclatural issues, patterns of biogeography, trends in floral morphology, and genome evolution can be examined. Few of the vanilloid orchid species take to cultivation. As a consequence, many are endangered or already extinct. It is imperative and warranted, therefore, that systematic research continues on this fascinating and pivotal group of orchids if their unique interactions with fungi and animal pollinators are to be understood before they are lost to habit destruction and overcollecting.