Contents I. II. III. IV. V. VI. VII. VIII. IX.
Cytoskeletal microtubules (
- NSF-PAR ID:
- 10451454
- Publisher / Repository:
- Published by Oxford University Press on behalf of American Society of Plant Biologists
- Date Published:
- Journal Name:
- The Plant Cell
- Volume:
- 35
- Issue:
- 5
- ISSN:
- 1040-4651
- Page Range / eLocation ID:
- 1496 to 1512
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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Summary Introduction MT arrays in plant cells γ‐Tubulin and MT nucleation MT nucleation sites or flexible MTOCs in plant cells MT‐dependent MT nucleation Generating new MTs for spindle assembly Generation of MTs for phragmoplast expansion during cytokinesis MT generation for the cortical MT array MT nucleation: looking forward Acknowledgements References Summary MT s) 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 theirMT 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 newMT s is a critical step forMT remodeling. Although many key factors contributing toMT nucleation and organization are well conserved in different kingdoms, the centrosome, representing the most prominent microtubule organizing centers (MTOC s), disappeared during plant evolution as angiosperms lack the structure. Instead, flexibleMTOC s may emerge on the plasma membrane, the nuclear envelope, and even organelles depending on types of cells and organisms and/or physiological conditions.MT ‐dependentMT nucleation is particularly noticeable in plant cells because it accounts for the primary source ofMT 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‐specificMTOC s and how plant cells activate or inactivateMT nucleation activities in spatiotemporally regulated manners. -
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The microtubule cytoskeleton serves as a dynamic structural framework for mitosis in eukaryotic cells. TANGLED1 (TAN1) is a microtubule-binding protein that localizes to the division site and mitotic microtubules and plays a critical role in division plane orientation in plants. Here, in vitro experiments demonstrate that TAN1 directly binds microtubules, mediating microtubule zippering or end-on microtubule interactions, depending on their contact angle. Maize tan1 mutant cells improperly position the preprophase band (PPB), which predicts the future division site. However, cell shape–based modeling indicates that PPB positioning defects are likely a consequence of abnormal cell shapes and not due to TAN1 absence. In telophase, colocalization of growing microtubules ends from the phragmoplast with TAN1 at the division site suggests that TAN1 interacts with microtubule tips end-on. Together, our results suggest that TAN1 contributes to microtubule organization to ensure proper division plane orientation.
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Abstract Formative asymmetric divisions produce cells with different fates and are critical for development. We show the maize (Zea mays) myosin XI protein, OPAQUE1 (O1), is necessary for asymmetric divisions during maize stomatal development. We analyzed stomatal precursor cells before and during asymmetric division to determine why o1 mutants have abnormal division planes. Cell polarization and nuclear positioning occur normally in the o1 mutant, and the future site of division is correctly specified. The defect in o1 becomes apparent during late cytokinesis, when the phragmoplast forms the nascent cell plate. Initial phragmoplast guidance in o1 is normal; however, as phragmoplast expansion continues o1 phragmoplasts become misguided. To understand how O1 contributes to phragmoplast guidance, we identified O1-interacting proteins. Maize kinesins related to the Arabidopsis thaliana division site markers PHRAGMOPLAST ORIENTING KINESINs (POKs), which are also required for correct phragmoplast guidance, physically interact with O1. We propose that different myosins are important at multiple steps of phragmoplast expansion, and the O1 actin motor and POK-like microtubule motors work together to ensure correct late-stage phragmoplast guidance.
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Introduction During proliferative plant cell division, the new cell wall, called the cell plate, is first built in the middle of the cell and then expands outward to complete cytokinesis. This dynamic process requires coordinated movement and arrangement of the cytoskeleton and organelles.
Methods Here we use live-cell markers to track the dynamic reorganization of microtubules, nuclei, endoplasmic reticulum, and endomembrane compartments during division and the formation of the cell plate in maize leaf epidermal cells.
Results The microtubule plus-end localized protein END BINDING1 (EB1) highlighted increasing microtubule dynamicity during mitosis to support rapid changes in microtubule structures. The localization of the cell-plate specific syntaxin KNOLLE, several RAB-GTPases, as well as two plasma membrane localized proteins was assessed after treatment with the cytokinesis-specific callose-deposition inhibitor Endosidin7 (ES7) and the microtubule-disrupting herbicide chlorpropham (CIPC). While ES7 caused cell plate defects in
Arabidopsis thaliana , it did not alter callose accumulation, or disrupt cell plate formation in maize. In contrast, CIPC treatment of maize epidermal cells occasionally produced irregular cell plates that split or fragmented, but did not otherwise disrupt the accumulation of cell-plate localized proteins.Discussion Together, these markers provide a robust suite of tools to examine subcellular trafficking and organellar organization during mitosis and cell plate formation in maize.
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Abstract Proper plant growth and development require spatial coordination of cell divisions. Two unrelated microtubule-binding proteins, TANGLED1 (TAN1) and AUXIN-INDUCED IN ROOT CULTURES9 (AIR9), are together required for normal growth and division plane orientation in Arabidopsis (Arabidopsis thaliana). The tan1 air9 double mutant has synthetic growth and division plane orientation defects, while single mutants lack obvious defects. Here we show that the division site-localized protein, PHRAGMOPLAST ORIENTING KINESIN1 (POK1), was aberrantly lost from the division site during metaphase and telophase in the tan1 air9 mutant. Since TAN1 and POK1 interact via the first 132 amino acids of TAN1 (TAN11–132), we assessed the localization and function of TAN11–132 in the tan1 air9 double mutant. TAN11–132 rescued tan1 air9 mutant phenotypes and localized to the division site during telophase. However, replacing six amino-acid residues within TAN11–132, which disrupted the POK1–TAN1 interaction in the yeast-two-hybrid system, caused loss of both rescue and division site localization of TAN11–132 in the tan1 air9 mutant. Full-length TAN1 with the same alanine substitutions had defects in phragmoplast guidance and reduced TAN1 and POK1 localization at the division site but rescued most tan1 air9 mutant phenotypes. Together, these data suggest that TAN1 and AIR9 are required for POK1 localization, and yet unknown proteins may stabilize TAN1–POK1 interactions.
