FAYETTEVILLE, Ark. — Cotton that produces its own insecticide and soybeans that can be sprayed with weed killer and survive, while the weed die, have become the most widely planted varieties of these major Arkansas crops.
Scientists have been able to isolate genes that produce pest and herbicide resistance and insert them into transgenic varieties of many of the world's most common food crops. Crops that once required multiple applications of chemical herbicides and insecticides now may only need one treatment per season, or none at all.
Transgenic varieties became available in the mid-1990s. In 2003, Arkansas farmers planted some 2.9 million acres of soybeans and 950,000 acres of cotton. Of that, 84 percent of the soybeans and 95 percent of the cotton were transgenic.
Now, researchers like Vibha Srivastava, an assistant professor with the University of Arkansas Division of Agriculture, are working to make this technology even better. Srivastava is developing new techniques for isolating and inserting beneficial genes that will make the development of transgenic crop varieties easier, more economical and more efficient.
"The conventional method of creating transgenic plants has several problems," Srivastava points out. "Most of the plants produced undergo a phenomenon known a 'gene silencing,' which can happen gradually or in the first generation. The gene is present in the cell, but it is not expressed, or it's expressed at a very low level. Because of this, we have to create very large populations of plants and then screen them over several generations to find the perfect specimen — one that contains the new gene, expresses it at the desired level, and continues to express it at that same level generation after generation."
The location of a gene on a chromosome and the pattern in which it is integrated into the host plant's DNA are major factors in determining how the gene will express. When DNA is inserted, it incorporates randomly to unpredictable locations, sometimes making multiple copies of itself, which causes problems with expression of the new gene.
"We want to be able to control the integration pattern of inserted DNA and direct it to a specific location," Srivastava says.
She is working with a couple of techniques to accomplish this. One involves using a two-step process of gene insertion, in which she inserts one DNA segment that acts as a target for a second DNA segment, which contains the new gene that she wants to incorporate. This method allows her to exercise greater control over where and how the new gene incorporates itself into the host plant.
The other technique uses a developing technology known as homologous recombination.
In homologous recombination, the new DNA sequence is inserted at a location where the host plant's DNA has a matching sequence. The new gene then "knocks out" the host's gene, and takes its place, increasing the odds of it being expressed and not silenced. However, this system does not work as well in practice as it should in theory.
"We are focusing on improving the efficiency of homologous recombination so that it can be used to improve the reliability of gene expression in various applications," Srivastava says.
Genetic engineering has already made a huge impact in the field of agriculture, and through the work of researchers like Srivastava, the production of genetically modified crops in the future promises to be easier and more accurate.
"The work that we are doing is not only restricted to plants, though," she says. "It's very basic work which will have applications throughout the whole field of genetics and biotechnology."
P.J. Hirschey, UA Department of Horticulture, [email protected]