Abstract
Genetic screening of Arabidopsis mutants defective in microtubule functions involves cell expansion mutants, helical growth mutants, and hypersensitive or resistant mutants to microtubule-targeted drugs. In Arabidopsis plants, roots, etiolated hypocotyls, petioles, and petals grow rapidly in highly anisotropic manner, and are more sensitive to dysfunctions of cortical microtubule organization and functions. Many helical growth mutants are caused by dominant-negative amino-acid-exchange-type mutations in α- or β-tubulins. Two right-handed mutants, spiral1 and spiral2, and a new drug-hypersensitive mutant propyzamide hypersensitive 2 (phs2), are loss-of-function mutants of distinct plant-specific microtubule regulators. A partial loss-of-function allele (spiral3) of GCP2, a core component of the γ-tubulin ring complex, stabilized the minus end of microtubules, producing a left-handed helical array. Molecular analysis of another mutant phs1-1 revealed a phosphorylation pathway in the regulation of microtubule dynamics. Recent progress involves biochemical and cell biological studies of these new members of microtubule regulators.
