DISSERTATION RESEARCH: Phylogenetically-Based Analysis of Plastid Genome Evolution in the Photosynthetically Variable Parasitic Flowering Plant Genus, Cuscuta

A grant has been awarded to Dr. Claude dePamphilis and Mr. Joel McNeal at Pennsylvania State University to study how different species of a group of parasitic plants known as dodders are related to each other and how genes that produce proteins necessary for photosynthesis differ between species in the lineage. Dodders, which are vines that possess only tiny, useless leaves and no roots whatsoever, attach to the stems of other plants and are dependent on these hosts for all of their water, inorganic nutrients, and most, if not all, of their carbohydrate needs. Because of this habit, the parasites have a reduced need to photosynthesize for themselves. Genes located within chloroplasts, the photosynthetic compartments of plant cells, are highly conserved across flowering plants because most of these genes are necessary for carbohydrate production from sunlight and atmospheric carbon dioxide. However, a large degree of variation exists in these genes between different dodders, indicating that different species may demonstrate differing abilities to photosynthesize.

By examining which genes are well conserved within chloroplasts of different dodder species and related non-parasitic plants, an understanding of which genes are most important for photosynthesis and which genes are more expendable will be gained. These data will be verified further by comparison with other parasitic plant lineages. Furthermore, knowledge of the relationships between dodder species may eventually prove to be valuable to the control of these parasitic weeds, many of which do serious agricultural damage and are federally designated noxious weeds. The transition from being nutritionally independent to being parasitic has occurred numerous times within plants and also within many other lineages of life. This parasitic plant group will serve as an excellent model to study the genetic changes that accompany this transition.