ALPHA-TUBULIN MISSENSE MUTATIONS CORRELATE WITH ANTIMICROTUBULE DRUG-RESISTANCE IN ELEUSINE INDICA

Dinitroaniline herbicides are antimicrotubule drugs that bind to tubul ins and inhibit polymerization. As a result of repeated application of dinitroaniline herbicides, highly resistant and intermediately resist ant biotypes of goosegrass (Eleusine indica) developed in previously w ild-type populations. Three alpha-tubulin cDNA classes (designated TUA 1, TUA2, and TUA3) were isolated from each biotype. Nucleotide differe nces between the susceptible and the resistant (R) alpha-tubulins were identified in TUA1 and TUA2. The most significant differences were mi ssense mutations that occurred in TUA1 of the R and intermediately res istant (I) biotypes. Such mutations convert Thr-239 to Ile in the R bi otype and Met-268 to Thr in the I biotype. These amino acid substituti ons alter hydrophobicity; therefore, they may alter the dinitroaniline binding property of the protein. These mutations were correlated with the dinitroaniline response phenotypes (Drp). Plants homozygous for s usceptibility possessed the wild-type TUA1 allele; plants homozygous f or resistance possessed the mutant tua1 allele; and plants heterozygou s for susceptibility possessed both wild-type and mutant alleles. Thus , we conclude that TUA1 is at the Drp locus. Using polymerase chain re action primer-introduced restriction analysis, we demonstrated that go osegrass genomic DNA can be diagnosed for Drp alleles. Although not di rect proof, these results suggest that a mutation in an alpha-tubulin gene confers resistance! to dinitroanilines in goosegrass.