Microtubule-associated protein that bundle and stabilize adjacent microtubules (MT) of the cell cortex. Enhances MT nucleation. Can also bind to tubulin dimers and promotes their polymerization. Confers MT resistance to the drug propyzamide and cold conditions. Plays a role in the central spindle at anaphase to early cytokinesis but is not essential at the midline of the phragmoplast at later stages. Represses metaphase spindle organization and the transition to anaphase in dephosphorylated active form. Promotes the formation of a planar network of antiparallel microtubules. May be involved in stomatal movement modulation by regulating the dynamic and arrangement of cortical MT. Forms dimer. Binds to MT, mostly with coaligned MT, both between parallel or antiparallel, forming thick bundles. Interacts with the alpha-tubulin subunit of the tubulin heterodimer. Bundles polymerized MT via the formation of 25-nm crossbridges at specific stages of the cell cycle (e.g. bundles microtubules in interphase, anaphase and telophase but does not bind microtubules in prophase or metaphase), at the plus-end, the minus-end, or along the entire length of MT, and along phragmoplast MT. Interacts with SH3P1 and MPK4. During interphase, binds cortical microtubules. In M-phase, locates to the preprophase band. Binds the preprophase band but does not accumulate at the prophase spindle microtubules that coexists within the same cell. In the metaphase and anaphase, localized to spindle. In the phragmoplast, concentrated at the midzone where vesicles guide by MT coalesce to form the cell plate. Present in MT cortical arrays. Concentrated in dots surrounding the nuclei. A number of isoforms are produced. According to EST sequences. Expressed in all organs and tissues with the exception of sepals and anthers. Bound to subsets of microtubules in the cells of root epidermis, hypocotyl and cotyledons (at protein level). Expressed throughout the cell cycle. Basal phosphorylation at all stages of the cell cycle. MT-binding properties inhibited by hyperphosphorylation mediated by CDKs and/or MAPKs (e.g. ANP2, ANP3, MPK4 and MPK6) during prometaphase and metaphase. Belongs to the MAP65/ASE1 family.