Abstract
In plant cells, cortical microtubule (MT) arrays generally regulate the direction of elongation. Analysis of right-handed and left-handed twisting Arabidpsis in our lab mutants provided supporting evidence.
When we tagged α-tubulin (TUA) at the N-terminus and expressed under the CaMV35S promoter in transgenic plants, it was incorporated into MT polymers and caused right-handed helical growth in petioles and petals. In contrast, TUA tagged at the C-terminus and β-tubulin tagged at the N-terminus did not produce helical phenotypes, although they were incorporated into MTs. We speculated that TUA with an extra sequence at the N-terminus interferes its GTPase activating function, leading to longer GTP cap and more stable microtubules, resulting in right-handed helical growth. To test this hypothesis, we examined the effect of TUA mutations which are predicted to be involved in this GTPase activation. Plants expressing the mutant tubulins caused right-handed helical growth, and had increased trichome branching.
