Microtubule nucleation for the assembly of acentrosomal microtubule arrays in plant cells

Abstract

Contents SummaryI.IntroductionII.MT arrays in plant cellsIII.γ‐Tubulin and MT nucleationIV.MT nucleation sites or flexible MTOCs in plant cellsV.MT‐dependent MT nucleationVI.Generating new MTs for spindle assemblyVII.Generation of MTs for phragmoplast expansion during cytokinesisVIII.MT generation for the cortical MT arrayIX.MT nucleation: looking forward AcknowledgementsReferences Summary Cytoskeletal microtubules (MTs) have a multitude of functions including intracellular distribution of molecules and organelles, cell morphogenesis, as well as segregation of the genetic material and separation of the cytoplasm during cell division among eukaryotic organisms. In response to internal and external cues, eukaryotic cells remodel their MT network in a regulated manner in order to assemble physiologically important arrays for cell growth, cell proliferation, or for cells to cope with biotic or abiotic stresses. Nucleation of new MTs is a critical step for MT remodeling. Although many key factors contributing to MT nucleation and organization are well conserved in different kingdoms, the centrosome, representing the most prominent microtubule organizing centers (MTOCs), disappeared during plant evolution as angiosperms lack the structure. Instead, flexible MTOCs may emerge on the plasma membrane, the nuclear envelope, and even organelles depending on types of cells and organisms and/or physiological conditions. MT‐dependent MT nucleation is particularly noticeable in plant cells because it accounts for the primary source of MT generation for assembling spindle, phragmoplast, and cortical arrays when the γ‐tubulin ring complex is anchored and activated by the augmin complex. It is intriguing what proteins are associated with plant‐specific MTOCs and how plant cells activate or inactivate MT nucleation activities in spatiotemporally regulated manners.

Establishment of a mitotic model system by transient expression of the D‐type cyclin in differentiated leaf cells of tobacco (Nicotiana benthamiana)

“…thaliana , we were able to visualize the intracellular localization pattern of proteins such as AtAUR1 in greater detail by focusing on individual mitotic apparatus. We also examined the augmin complex, which acts along spindle MTs to generate new MTs for spindle MT reorganization during mitosis (Lee & Liu, ). It was reported that augmin's function in mitosis is defined by its mitotic‐specific, MT‐associated protein subunit AtEDE1 (Endosperm Defective1) (Pignocchi et al , ; Lee et al , ).…”

The γ-tubulin complex protein GCP6 is crucial for spindle morphogenesis but not essential for microtubule reorganization inArabidopsis

“…The gcp6 mutant exhibited a striking phenotype in MT organization at prophase. Typically, MTs are organized into a bipolar prospindle array with well-defined and focused poles decorated by γ-tubulin in a pattern described as the polar cap (43). Without the γTuRC in the absence of GCP6, ample MTs were still produced but did not form polar caps.…”

Microtubule organization defects in Arabidopsis thaliana

“…1995) and the protofilament model (Erickson & Stoffler 1996). In particular, γ‐tubulin is considered an essential MT‐nucleating factor (Lee & Liu 2019). Its homologous genes are present in all eukaryotes and are also found to be one of the core components in γ‐tubulin complex proteins (GCP).…”

“…Generally, increase and elongation of MT are achieved through α‐ and β‐tubulin via spiral layers in eukaryotic cells (Wu & Akhmanova 2017). In addition, the dynamic behaviour of MT, associated with various MT‐associated proteins (MAP), generates MT arrays that are utilized by eukaryotic cells as the pathway for cell migration and intracellular movement, as well as for spindle assembly and signal transduction during cell division (Lee & Liu 2019). For example, the MT cytoskeleton plays an important role in cell morphology, the spatial distribution and migration of organelles, intracellular transport, signal transduction and the regulation of cell division in Arabidopsis (Struk & Dhonukshe 2014).…”