Current Research Projects at the Center for Plant Biotechnology Research
College of Agricultural, Environmental, and Natural Sciences, Tuskegee University 6nov00

The Center continues along the tradition of George Washington Carver, the legendary scientist who developed hundreds of innovative products from sweetpotato and peanut working at Tuskegee University earlier this century. Sweetpotato is nutritionally and economically very important to many people around the world especially those with limited resources, and is the fourth largest crop in the developing world. Sweetpotato produces more calories and protein per ha per day than most other crops, and requires very little input. Genetic engineering has the potential to rapidly improve sweetpotato as conventional breeding techniques are difficult to apply in this crop due to poor seed set and sterility of flowers.

Sweetpotato Tissue Culture

Our efforts were focused initially on identifying methods to deliver foreign genes into sweetpotato using gene gun and Agrobacterium approaches. An important pre-requisite for developing transgenic plants in any crop is the availability of tissue culture methods to regenerate whole plants from transformed cells. Although we developed methods to produce adventitious plants efficiently in vitro , our success in developing transgenic sweetpotato owes in large measure to the development of a high-frequency somatic embryogenesis protocol and the identification of highly regenerable cultivars in our Center. John Rasheed Bennett (an undergraduate student) is aiming to further improve this method using a novel cyclical approach.

Transgenic Plants

Genetically engineered sweetpotato plants with marker genes developed at the Center have now been studied under greenhouse and hydroponic conditions, and the expression patterns of foreign genes have been characterized. Soon, we will be testing transgenic sweetpotao plants with herbicide resistance genes under field conditions.

As sweetpotato plays a critical role in the diet of children in many developing countries in Africa, Asia and South Pacific, an improvement in the protein quality of this crop may have a positive impact on the health and nutrition of these people. In a study funded by NASA, Marceline Egnin has engineered sweetpotato plants with an artificial storage protein (ASP-1) gene developed by Dr. Jesse Jaynes of Demeter Biotechnologies Inc. Ragonva Walls, a graduate student, has also introduced rice chitinase and alfalfa glucanase genes into sweetpotato and has developed transgenic plants with a potential for fungal resistance in a project supported by USDA under the 1890 Institution Capacity Building Grants Program. These transgenic plants will soon be tested for amino acid composition and for disease resistance. We are also attempting to develop sweetpotatoes with resistance to feathery mottle virus using the coat protein genes of the virus in collaboration with Dr. Roger Beachy of ILTAB/Scripps Research Institute. As it is critical to express the disease and pest resistance genes in a tissue-specific manner, David Scott has cloned many genes from the periderm of sweetpotato roots with a grant from National Science Foundation. The goal is to identify regulatory regions from such genes and employ these promoters to preferentially express certain resistance genes in the skin of sweetpotato storage roots.

As sweetpotato has very high biomass output and is grown widely, it has considerable potential for mass production of novel compounds in an inexpensive manner through genetic engineering. In collaboration with Dr. Henry Daniell of Auburn University, Ramanjini Gowda is developing and testing sweetpotato plants producing biopolymers. These protein-based polymers have considerable medical applications and because of their rapid biodegradability, are very useful in the production of environmentally-friendly plastics in a renewable manner as opposed to the petroleum-based products.

The most exciting plant biotechnology development in the past year is the production of oral vaccines in plants by expressing antigens from human pathogens. Employing the genes obtained from Dr. Charles Arntzen of Boyce Thompson Plant Research Institute, Ramanjini Gowda and Agnes Kilonzo are developing transgenic sweetpotato, peanut and muskmelon plants to produce edible vaccines against the diarrhea caused by E. coli and cholera pathogen. Similarly, oral vaccine against rabies is also under development in these crops in a collaborative effort by Gowda and Xiaoping Zhu with Dr. Peter McGarvey and Dr. Hilary Koprowski of Thomas Jefferson Institute. As high expression and appropriate targeting of foreign proteins is necessary to ensure the success of edible vaccine production in plants, Jacquelyn Jackson (an undergraduate student) is testing various new promoters, enhancers and signal sequences in sweetpotato using green fluorescent protein (GFP) as a marker gene. The GFP gene, originally cloned form the jelly fish, has high potential in plant biology research because it can be detected without destroying the plant tissues and without using any substrates.

Polymorphic DNA markers are proving to be invaluable in plant genetic research because of their applications in the development of genetic maps, gene tagging, cloning useful genes and in studying genetic diversity. The Center for Plant Biotechnology Research scientists (Guohao He) have employed the DNA amplification fingerprinting (DAF) technique to study the genetic diversity of sweetpotato varieties from around the world and to fingerprint U. S. sweetpotato cultivars. A visiting scientist from Beijing Agricultural University (Wang Jiaxu) is now using this approach at the Center to characterize the Chinese sweetpotato germplasm. We have also identified polymorphic DNA markers for the first time in cultivated peanut using the DAF approach and the new Amplified Fragment Length Polymorphism (AFLP) technique. We are currently employing these novel markers to gain insights into genetic variability patterns and evolutionary relationships among various botanical varieties of peanut obtained from various locations in South America, the home of cultivated peanut (Martis Watts). In a collaborative research with Dr. George Bruening of University of California, Davis we are employing AFLP technique to locate a marker linked to the cowpea mosaic virus resistance gene using near-isogenic lines. The AFLP markers are also being employed to investigate the genetic diversity among cowpea germplasm subset from IITA, Nigeria in a study funded by AID. A technician from IITA will soon be trained in the DNA marker techniques and Dr. Ng, germplasm botanist at IITA will be a visiting scientist at the Center under this project. Scholars and students from many developing countries such as Ghana, Tanzania, Zaire, Swaziland, Cote d' Voire, China, India, and Dominican Republic have also received training in genetic engineering techniques at the Center.

A major mission of the Center is to train minority students in plant biotechnology and this is critical considering there are so few African-American or Hispanic molecular biologists. Several minority graduate and undergraduate students are provided with research assistantships and an opportunity to work on biotechnology projects. Similarly, high school students are offered summer internships to work in the laboratories and participate in research projects. This has proved very successful in enticing young minorities to consider a career in science. Recently, Ms. Natalie Knight of local high school has published a scientific paper along with the Center scientists in Molecular Biotechnology. Mr. Emitt Jolly who worked as a high school student in the Center a few years earlier to learn recombinant DNA techniques, has recently published an article in Science from an undergraduate internship research he conducted at the University of California, San Francisco.