MINICHROMOSOMES: THE NEXT GENERATION TECHNOLOGY FOR PLANT GENETIC ENGINEERING
Genetic transformation occurs frequently in nature in prokaryotes. The transfer of genes from one organism to another is termed horizontal gene transfer1. For example, bacteria can acquire virulence factors, as well as antibiotic resistance genes, which may lead to the breakdown of the efficacy of antibiotics. Horizontal gene transfers are rare in higher eukaryotes, but years ago scientists found that a pathogenic bacterium, Agrobacterium, could transfer genes from its genome to its plant hosts, where expression of the transferred genes caused crown gall disease2.
The development of Agrobacterium-mediated genetic transformation, and direct transformation by biolistics, i.e., the high velocity delivery of DNA attached to metal particles, led to the first generation of transgenic plants and the rapid application of this technology to crop improvement.
Genetic engineering as a driving force for modern agriculture
Genetic engineering is a powerful tool for improving crop quality and productivity, and reducing labor and resource utilization of farming. For example, farmers saved up to an estimated 60% of costs for pest control by growing Bt (insect resistance) cotton in certain regions of the US in 1997, according to a USDA report3. The reduction of pesticide spray has other safety benefits for both the environment and humans. Because of these and other benefits, the adoption of three primary GE crops (corn, cotton and soybean) for two traits, HT (herbicide tolerance) and Bt, has dramatically increased since the first commercial introduction in 1996. According to recent USDA survey data (http://www.ers.usda.gov/Data/biotechcrops/), the acreage of GE soybeans reached 89% in the US in 2006, followed by 83% for cotton, and 61% for corn. Although most of the current GE crops are either herbicide