SPIRAL2 Controls Direction of Cell Expansion by Way of Microtubule Regulation

Abstract

In growing plants, cortical microtubule array plays an important role in regulating the direction of cell expansion. Arabidopsis spiral2/tortifolia1 (spr2) mutants showed exaggerated left-handed helical arrays of cortical microtubules and right-handed helical growth in epidermis of etiolated hypocotyl. The SPR2 gene encodes a plant-specific protein containing 894 amino acids. Overexpressed SPR2-GFP fusion protein rescued spr2 phenotypes and localized to microtubules. Tobacco SPR2 homologue was detected in microtubule-associated protein fractions purified from tobacco BY-2 cells by anti-SPR2 antiserum and LC/MS/MS analysis. Furthermore, purified recombinant SPR2 protein derectly bound to microtubules in vitro. We will report how SPR2 protein influences microtubule dynamics in vivo and in vitro.