Abstract
Transversely oriented cortical microtubule arrays have been proposed to be required for straight cell elongation. In elongating epidermal cells of Arabidopsis thaliana spiral3-1 (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 Grip84 which is a component of the gamma-tubulin complex (γ-TuC) and spr3-1 mutant has an amino acid substitution mutation in a highly conserved Grip motif. Yeast two-hybrid assays indicated that spr3-1 mutation impairs interaction with AtGrip91, another component of γ-TuC. Cortical microtubules are nucleated as branches on the pre-existing microtubules. The angles of branching in spr3-1 cells were altered from those in wild-type cells. We also observed differences in minus end microtubule dynamics between the wild-type and mutant cells.
Our results indicate that a defect in microtubule nucleation leads to alteration in array organization, by affecting dynamics of cortical microtubules.
