Mary Rumpho-Kennedy

Education

PhD Washington State University

Description

Professor of Biochemistry. As a plant physiologist/biochemist, my research focuses on the unusual endosymbiotic association between algal (Vaucheria litorea) chloroplasts and a marine mollusc (Elysia chlorotica), resulting in photosynthetic sea slugs. My lab is conducting research to characterize the symbiont plastids and demonstrate horizontal gene transfer between the algal nucleus and the sea slug. In addition, we are exploring the possibility that the sea slug produces anti-cancer metabolites as an anti-predator defense mechanism.

Research interests

Solar-Powered Sea Slugs. The major project in my lab focuses on a unique solar-powered sea slug, Elysia chlorotica. This sea slug has evolved the means to carry out photosynthesis as a result of forming a symbiotic (kleptoplastic) association with chloroplasts it steals from its algal food source, the heterokont alga Vaucheria litorea. The captured chloroplasts (kleptoplasts) remain functional in cells lining the sea slug’s expansive digestive tract. The dark green animals subsist photoautotrophically and reproduce in culture, apart from any additional algal food source, for the duration of their normal 9 to 10 month life span. The chloroplasts have not yet been integrated into the germline, hence, the association must be established anew with each generation.

We have succeeded in rearing sea slugs from eggs and establishing the obligate chloroplast association by providing juvenile sea slugs with filaments of V. litorea. We are examining the uptake and establishment of the symbiotic association using various microscopical approaches and live animal feeding; video-and still-images of the act of establishment have been recorded. To date, no algal nuclei have been detected within the cells of the mollusc. This begs one to ask how oxygenic photosynthesis can be maintained without the large number of chloroplast proteins encoded in the genes of the algal nucleus. In an attempt to find these genes elsewhere, we first sequenced the chloroplast genome of V. litorea and the mitochodnrial genome of E. chlorotica, but neither revealed any unusual coding capacity to suggest any greater autonomy of these organelles than other secondary endosymbionts. We are now focused on identifying if algal nuclear genes encoding chloroplast proteins have been transferred from the alga to the sea slug over the course of evolution. We have targeted the Calvin Cycle enzyme phosphoribulokinase (PRK), and the manganese stabilizing protein (MSP, psbO), an essential component of the photosystem II oxygen evolving complex. Using PCR and qRT-PCR and V. litorea homologous primers, we were able to demonstrate the presence and expression of both genes in sea slugs and sea slug eggs with very high similarity to the corresponding algal sequences. Two copies of prk were detected in sea slug DNA and cDNA, one with and one without an intronic sequence found in the algal genomic prk sequence. We are currently employing high-throughput genomics and transcriptomics to determine the degree of HGT, and to demonstrate where/how the DNA has been integrated within its new host. In addition, we are initiating a proteomics study of the captured plastids to identify which proteins are still found in the plastids after several months of "starvation" (no algal food source) in E. chlorotica.

Fascinating organisms like these "solar-powered sea slugs" can transform the teaching of basic principles in biology. We are exploiting the sea slugs in the development of multimedia educational materials disseminated through an interactive Web site (http://sbe.umaine.edu/symbio/), and partially funded by the American Society of Plant Biologists and the Maine Technology Institute. Culturing of the sea slugs will ultimately provide a supply of this unusual organism for classrooms and laboratories, marine aquaria hobbyists, and contributes to protection of a rare species and its native habitat.

Elysia chlorotica and Vaucheria litorea.  A) Dorsal view of E. chlorotica.  Animals are typically found in nature as small as 1 or 2 cm to as large as 6 cm, as shown here.  B) Ventral view of E. chlorotica.  C) Two camouflaged E. chlorotica specimens feeding on V. litorea.  D) Several specimens of E. chlorotica showing the variation in size and body forms.  E) V. litorea filaments (about 1 to 2 mm diameter).  F) Sea slugs are easily cultured in aquaria containing full-strength artificial sea water and overhead lighting at 10°C.  Non-pigmented eggs are produced in a mucus mass on the aquaria walls (see arrow).  The eggs serve as a source of pure animal DNA since no plastids are found in the eggs.

Biosynthesis of Natural Anticancer Compounds in Molluscs. The sea slug Elysia chlorotica is also being exploited for its natural production of anticancer compounds as a predatory defense. Several species of ascoglossan molluscs, including members of the algal feeding genus Elysia, have been shown to synthesize and accumulate toxic secondary metabolites in their mucus which they subsequently can secrete in large amounts as a defense mechanism.  Some of these compounds have been shown to possess anticancer activity and one of these, a cyclic depsipeptide named kahalalide F, is in preclinical lung and colon cancer trials by PharmaMar in Spain. We are exploring extracts of the sea slugs and copious mucus produced by E. chlorotica to identify any secondary metabolites which may exhibit antifungal or anticancer properties against human cancer cell lines.  If such metabolites are found, the algal food source Vaucheria litorea, will also be analyzed as well as sea slug eggs which are devoid of any plastids.  This will tell us if synthesis of the toxic metabolites is dependent on the symbiotic association with the plastids and perhaps a driving force behind the symbiotic evolutionary adaptation.    

New England Invasive Plant Center. A second project area in my lab focuses on noxious invasive plants which cause at least a $35 billion loss per year to the U.S. economy. This figure is increasing at a rate of 10% annually. Because of the urgent need for new and effective approaches to address the serious problem of invasive plants, which include many ornamental crops, the University of Maine, the University of Connecticut, and the University of Vermont requested and received funding from the USDA to establish a multi-state, interdisciplinary New England Invasive Plant Center. Using its strength in developing non-invasive ornamental plants, the Center is focused on novel strategies to manage problems caused by invasive plants that are economically and environmentally damaging to the Northeastern U.S. and to the nation as a whole. The proposed objectives for the Center are: 1) Development of non-invasive sterile landscape plants. 2) Assessment of the ecological impact of invasive plants and ecological evaluation of new “super-sterile” cultivars. 3) Assessment of the economic impact of invasive species in New England and 4) Development of alternative native crops.

Our research focuses specifically on the invasive plant Japanese barberry in Acadia National Park (ANP), Maine. We are using high-throughput 16S rDNA amplicon and ITS amplicon sequencing to identify the bacterial and fungal symbionts, respectively, associated with Japanese barberry in the soil. The results from ANP are being compared with results from native Japanese barberry soils in Japan.

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Publications

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