Abstract
Transversely oriented cortical microtubule arrays have been proposed to be required for straight cell elongation.
The Arabidopsis thaliana spiral3-1 (spr3-1) mutants are useful for studying interactions between microtubule organization and nucleation. In elongating epidermal cells of spr3-1 roots, cortical microtubules were arranged in shallow left-handed helical arrays, in contrast to wild-type transverse arrays. The SPR3 protein is a homologue of gamma ring protein 84 (Grip84) and spr3-1 mutant has an amino acid substitution mutation in a highly conserved grip motif. In fungi and animal cells, Grip84 is a component of the gamma-tubulin ring complex (γ-TuRC) which shows core nucleating activity of microtubules. Yeast two-hybrid assays indicated that spr3-1 mutation impairs interaction with AtGrip91, another component of γ-TuRC.
Our results indicate that a defect in microtubule nucleation leads to alteration in array organization, possibly by affecting dynamics of cortical microtubules.
