REU: Molecular Systematics of the Legume Tribe Phaseoleae and Allies

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The Phaseoleae is the largest taxonomic tribe of the legume family. Among the more than 80 genera of the tribe are a number of familiar food plants including the garden bean, lima bean, soybean, hyacinth bean, pigeon pea, cowpea, mungbean, and jack bean. Despite the economic importance of the tribe, relationships among the genera are in most cases poorly known. Three levels of systematic questions will be addressed by Dr. Jeffrey Doyle of Cornell University in this project: 1) what are the natural grouping of genera? 2) how are natural groups of genera related to one another? and 3) is the tribe as a whole a natural, monophyletic group? This third question has important implications for the phylogeny of the entire papilionoid (bean) subfamily of the Leguminosae, because the tribal taxonomy is based largely on a few key morphological characters of dubious validity. Thus to address the third question, groups outside the Phaseoleae will also be studied. The characters to be analyzed in the research are molecular in nature. Preliminary work has shown that two major structural mutations of chloroplast DNA (cpDNA) will be useful for the circumscription of groups of genera at the levels of subtribe within the Phaseoleae and of groups of tribes related to the woody Millettieae. An insertion sequence in a storage protein gene characterizes the soybean and its close relatives. A duplication for the gene encoding cytosolic glucosephosphate isomerase has been silenced in various members of the Phaseoleae. The first stage of the project, therefore, will be to use such rare mutations to delimit groups of taxa, affording at least partial answers to the questions posed. Once natural groups are defined, precise relationships among genera can be studied by such techniques as cpDNA mapping and the sequencing of particular genes.