INTRODUCTION
During evolution of the plant kingdom, loss of motility was concomitant with loss of structured microtubuleorganizing centres and dispersal of microtubule nucleation complexes at various cellular locations (Leander and Yubuki, 2013). Vascular plant cell division is characterized by open mitosis, during which cytoplasmic microtubules (MTs) organize into a bipolar mitotic spindle. As cells cannot move and reorganize themselves within a tissue due to the presence of their cell wall, spindle polarity is essential for plant morphogenesis. The position of development of the future cell plate is forecast in G2 phase by the formation and narrowing of a transient preprophase band (PPB) of cortical microtubules, originally described at the ultrastructural level by PickettHeaps (1969). Some of these dynamic polymers converge to the nuclear poles, linking the poles to the cortex (Wick and Duniec, 1983; Gunning and Wick, 1985). In addition, perinuclear MTs radiating towards the cytoplasm increase in density, indicating initiation of new MT nucleation events. These microtubular arrays are completely reorganized from G2 to metaphase, starting with formation of a pro-spindle and ending with the metaphase plate, which corresponds to an equilibrium state before chromatid segregation. In order to decipher the mechanisms involved in spindle formation, various methodological approaches have been used, such as immunocytochemistry, use of cytoskeleton drugs, expression of fluorescent fusion proteins combined with purification of protein complexes, and genetic studies. This review summarizes current knowledge regarding the proteins and protein complexes involved in the successive steps leading to formation of a robust functional spindle in vascular plants.