HERBICIDE RESISTANCE CAUSED BY SPONTANEOUS MUTATION OF THE CYTOSKELETAL PROTEIN TUBULIN

The dinitroaniline herbicides (such as trifluralin and oryzalin) have been developed for the selective control of weeds in arable crops. How ever, prolonged use of these chemicals has resulted in the selection o f resistant biotypes of goosegrass, a major weed. These herbicides bin d to the plant tubulin protein but not to mammalian tubulin(1). Here w e show that the major alpha-tubulin gene of the resistant biotype has three base changes within the coding sequence. These base changes swap cytosine and thymine, most likely as the result of the spontaneous de amination of methylated cytosine. One of these base changes causes an amino-acid change in the protein: normal threonine at position 239 is changed to isoleucine. This position is dose to the site of interactio n between tubulin dimers in the microtubule protofilament. We show tha t the mutated gene is the cause of the herbicide resistance by using i t to transform maize and confer resistance to dinitroaniline herbicide s. Our results provide a molecular explanation for the resistance of g oosegrass to dinitroanaline herbicides, a phenomenon that has arisen, and been selected for, as a result of repeated exposure to this class of herbicide.