Genetic Engineering of Herbicide Resistance Genes

Abstract

The ability to integrate functional genes stably into a plant genome not only offers a powerful approach to address the fundamental questions of developmental gene expression but also provides valuable opportunities for crop improvement (for reviews, see Fraley et al., 1986; Goodman et al, 1987). Exciting progress has been made during the last four years in the identification and transfer of genes that confer resistance to plant viruses and insect pests. Gene transfer has also been used to engineer resistance to nonselective, environmentally safe herbicides. Over the past several years, the use of herbicides has become an established practice in world agriculture. By eliminating weeds that compete with crops for water and nutrients, herbicides increase the crop yield. New highly potent herbicides have been developed that inhibit plant growth by interfering with the biosynthesis of essential amino acids, rather than by inactivating a component of the photosynthetic apparatus (Table 1) (LaRossa and Falco, 1984). These structurally unrelated herbicides include: glyphosate which inhibits the synthesis of aromatic amino acids; the sulfonylurea and imidazolinone herbicides which block branched chain amino acid biosynthesis; and phosphinothricin which inhibits glutamine biosynthesis. Although potent and environmentally safe, these herbicides have broad-spectrum activity that discriminates poorly between weeds and crops. The genetic engineering of selective resistance to these herbicides in crop species will have substantial agronomic significance and has been the major focus of research in several labs.