An Arabidopsis thaliana tubulin mutant with conditional root-skewing phenotype

Low doses of microtubule-interacting drugs cause wild-type Arabidopsis thaliana seedling roots to twist in a left-handed helical direction. We here report molecular characterization of an A. thaliana tubulin mutant whose roots twist in a right-handed direction and have shallow left-handed cortical microtubule arrays when challenged with low doses of microtubule drugs. In the absence of the drug, growth and development of the mutant was apparently normal. In this conditional twisting mutant, Cys213 of alpha-tubulin6 was exchanged with Tyr. The mutant tubulin was incorporated into the microtubule polymer with wild-type tubulins, and thus acted as a dominant-negative mutation. These results suggest that compromised microtubules in wild-type and mutant roots are qualitatively distinct and affect skewing direction differently.