Hairy roots are a type of tumor that forms on plants infected by the soil bacterium Agrobacterium rhizogenes. By inserting a specific gene into the bacterium, researchers can integrate that gene into the host plant's DNA. Eventually, the host develops a system of fuzzy-looking roots near the site of the infection. These so-called "hairy roots" are transgenic, meaning they contain the genes of both the host plant and the bacterium.

Scientists believe they can create hairy roots that churn out the product of inserted genes with a stability and productivity not possible with most other plant cell cultures. San '78, Rice's E.D. Butcher Professor of Bioengineering, said scientists have long wanted to harness the production prowess of hairy roots for industry, but first they must determine the long-term stability of the genetically altered roots.

"The species of periwinkle that we're studying produces a wide variety of alkaloids -- including the anti-cancer drugs vincristine and vinblastine," said study co-author Ka-Yiu San. "Hairy roots have a number of advantages over cell cultures as a production platform for these compounds."

In the new study, San and Rice graduate student Christie Peebles described the methods they used to keep a transgenic hairy root culture alive for 4-and-a-half years. At the outset, they infected a periwinkle plant with a bacterium carrying a gene for fluorescence. By transferring root tips into fresh liquid every four weeks, they maintained a stable root culture that had the characteristic fluorescent glow produced by the gene.

Ultimately, San and his collaborators hope to make genetic modifications to the metabolic pathways of the transgenic periwinkle roots, changes that will allow them to produce far more vincristine and vinblastine than is normally produced by a regular periwinkle plant.

Study co-authors include Iowa State University's Jacqueline Shanks, adjunct professor of bioengineering at Rice, and plant biologist Susan Gibson of the University of Minnesota.

- Rice University