From the archives: Roles of microtubule-associated proteins in organelle movement, tip growth, and phragmoplast architecture

Microtubules are the largest cytoskeletal filaments that regulate the shape and internal organization of the eukaryotic cell. They are composed of tubulin dimers polymerized around a hollow core and undergo rapid cycles of assembly and disassembly. They are intrinsically polar, with a fast-growing plus end and a slow-growing minus end. New microtubules are formed by a process called nucleation. In plants, nucleation occurs primarily on the walls of existing microtubules such that the nascent microtubules appear branched at particular angles. Many microtubule-associated proteins regulate microtubule dynamics by nucleation, stabilization, destabilization, capping, or cross-linking. Kinesins are ATP-dependent motor proteins that move along microtubules to transport cargoes such as vesicles and organelles. Their motility can be assessed in vitro by the gliding assays, wherein surface-immobilized motor proteins propel microtubules to glide over a glass slide. Investigations on microtubule-associated proteins provide insights into their roles during various cellular processes, as exemplified below.