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1. Helical growth of twining common bean is associated with longitudinal, not skewed, microtubule patterning

   https://doi.org/10.1093/jxb/eraf512  

   Acevedo, Angelique A; Sousa-Baena, Mariane S; Onyenedum, Joyce G (November 2025, Journal of Experimental Botany)

   Murray, James (Ed.)

   Abstract Organ chirality in plants has been linked to cytoskeletal organization, as demonstrated in Arabidopsis twisted mutants, where left-skewed cortical microtubules are associated with right-handed twisting, and vice versa. While this phenotype seemingly mirrors vining habits, the hypothesis remains understudied within naturally twining plants. Qualitative observations have identified skewed microtubules in the twining stem of Ipomoea nil (L.) Roth vine, suggesting parallels with Arabidopsis studies. To further investigate organ chirality in twining plants, we used common bean vine (Phaseolus vulgaris L.) to examine the relationship between microtubule orientation, cell morphogenesis, and the right-handed twining phenotype via immunolabeling techniques. Here, we report a transition from mixed microtubule orientations in emergent and elongating internodes to a predominance of longitudinal microtubules in straight and twined stem segments post-elongation. Additionally, we report a distinction in epidermal cell shapes, where straight portions of the stem consist of lobes with rectangular cells and furrows with round cells, while twined portions comprise cells that are relatively more rectangular and stretched. We propose that these orientations reflect dynamic microtubule responses to external stimuli and growth cues, such as tensile stresses from climbing or tissue expansion. Taken together, these findings highlight dissimilarities between twisting Arabidopsis mutants and naturally twining plants. 

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2. Arabidopsis AUGMIN8 Contains Two Independent Microtubule Association Domains

   https://doi.org/10.1002/cm.70068  

   Chana, Naveen K; Cioffi, Timothy; Shaw, Sidney L (November 2025, Cytoskeleton)

   ABSTRACT Plant cells create a plasma membrane‐associated network of microtubules that are nucleated by γ‐tubulin ring complexes primarily through microtubule‐dependent microtubule nucleation (MDMN). This dynamic array organizes into specific patterns in response to developmental and environmental cues to influence primary cell wall construction. The molecular mechanisms directing the creation of cortical microtubule array patterns are largely unknown. The hetero‐octameric AUGMIN complex facilitates mitotic spindle formation by associating γ‐tubulin ring complexes with existing spindle microtubules and creating parallel branched microtubules through MDMN. AUGMIN8, the key linker protein connecting the AUGMIN complex to the parent microtubule, is encoded by a paralogous family of QWRF genes in flowering plants. Members of the QWRF family are distinguished by an unstructured N‐terminal half encoded in a single 5′ exon. We hypothesize that the QWRF paralogs form interchangeable AUGMIN microtubule binding subunits that confer specific roles to the AUGMIN complex in mitotic and non‐mitotic microtubule arrays. We identify four QWRF family members expressed inArabidopsishypocotyl cells and investigate the sites of QWRF interaction with cortical microtubules using transient transformation of fluorescently tagged constructs in the heterologousNicotiana benthamianasystem. We show that full‐length QWRF8 and QWRF4 associate with non‐mitotic, cortical microtubules as distributed puncta where QWRF8 shows evidence for two independent sites of microtubule association. Sequence comparisons and in vivo assay with homologous fragments from QWRF1, 2, 4, and 5 define a shared N‐terminal conserved microtubule association domain. We additionally identify protein regions leading to the formation of microtubule‐associated “QWRF bodies” potentially linked to discontinuous localization on microtubules. We identify the “QWRF” protein motif as a conserved domain associating the AUGMIN8 paralogs with AUGMIN6, part of the larger AUGMIN complex. 

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3. SSNA1 stabilizes dynamic microtubules and detects microtubule damage

   https://doi.org/10.7554/eLife.67282  

   Lawrence, Elizabeth J; Arpag, Goker; Arnaiz, Cayetana; Zanic, Marija (December 2021, eLife)

   Sjögren’s syndrome nuclear autoantigen-1 (SSNA1/NA14) is a microtubule-associated protein with important functions in cilia, dividing cells, and developing neurons. However, the direct effects of SSNA1 on microtubules are not known. We employed in vitro reconstitution with purified proteins and TIRF microscopy to investigate the activity of human SSNA1 on dynamic microtubule ends and lattices. Our results show that SSNA1 modulates all parameters of microtubule dynamic instability—slowing down the rates of growth, shrinkage, and catastrophe, and promoting rescue. We find that SSNA1 forms stretches along growing microtubule ends and binds cooperatively to the microtubule lattice. Furthermore, SSNA1 is enriched on microtubule damage sites, occurring both naturally, as well as induced by the microtubule severing enzyme spastin. Finally, SSNA1 binding protects microtubules against spastin’s severing activity. Taken together, our results demonstrate that SSNA1 is both a potent microtubule-stabilizing protein and a novel sensor of microtubule damage; activities that likely underlie SSNA1’s functions on microtubule structures in cells. 

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4. More is different: Reconstituting complexity in microtubule regulation

   https://doi.org/10.1016/j.jbc.2023.105398  

   Lawrence, Elizabeth J; Chatterjee, Saptarshi; Zanic, Marija (December 2023, Journal of Biological Chemistry)

   Microtubules are dynamic cytoskeletal filaments that undergo stochastic switching between phases of polymerization and depolymerization—a behavior known as dynamic instability. Many important cellular processes, including cell motility, chromosome segregation, and intracellular transport, require complex spatiotemporal regulation of microtubule dynamics. This coordinated regulation is achieved through the interactions of numerous microtubule-associated proteins (MAPs) with microtubule ends and lattices. Here, we review the recent advances in our understanding of microtubule regulation, focusing on results arising from biochemical in vitro reconstitution approaches using purified multiprotein ensembles. We discuss how the combinatory effects of MAPs affect both the dynamics of individual microtubule ends, as well as the stability and turnover of the microtubule lattice. In addition, we highlight new results demonstrating the roles of protein condensates in microtubule regulation. Our overall intent is to showcase how lessons learned from reconstitution approaches help unravel the regulatory mechanisms at play in complex cellular environments. 

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5. Analysis of formin functions during cytokinesis using specific inhibitor SMIFH2

   https://doi.org/10.1093/plphys/kiab085  

   Zhang, Laining; Smertenko, Tetyana; Fahy, Deirdre; Koteyeva, Nuria; Moroz, Natalia; Kuchařová, Anna; Novák, Dominik; Manoilov, Eduard; Smertenko, Petro; Galva, Charitha; et al (February 2021, Plant Physiology)

   Abstract The phragmoplast separates daughter cells during cytokinesis by constructing the cell plate, which depends on interaction between cytoskeleton and membrane compartments. Proteins responsible for these interactions remain unknown, but formins can link cytoskeleton with membranes and several members of formin protein family localize to the cell plate. Progress in functional characterization of formins in cytokinesis is hindered by functional redundancies within the large formin gene family. We addressed this limitation by employing Small Molecular Inhibitor of Formin Homology 2 (SMIFH2), a small-molecule inhibitor of formins. Treatment of tobacco (Nicotiana tabacum) tissue culture cells with SMIFH2 perturbed localization of actin at the cell plate; slowed down both microtubule polymerization and phragmoplast expansion; diminished association of dynamin-related proteins with the cell plate independently of actin and microtubules; and caused cell plate swelling. Another impact of SMIFH2 was shortening of the END BINDING1b (EB1b) and EB1c comets on the growing microtubule plus ends in N. tabacum tissue culture cells and Arabidopsis thaliana cotyledon epidermis cells. The shape of the EB1 comets in the SMIFH2-treated cells resembled that of the knockdown mutant of plant Xenopus Microtubule-Associated protein of 215 kDa (XMAP215) homolog MICROTUBULE ORGANIZATION 1/GEMINI 1 (MOR1/GEM1). This outcome suggests that formins promote elongation of tubulin flares on the growing plus ends. Formins AtFH1 (A. thaliana Formin Homology 1) and AtFH8 can also interact with EB1. Besides cytokinesis, formins function in the mitotic spindle assembly and metaphase to anaphase transition. Our data suggest that during cytokinesis formins function in: (1) promoting microtubule polymerization; (2) nucleating F-actin at the cell plate; (3) retaining dynamin-related proteins at the cell plate; and (4) remodeling of the cell plate membrane. 

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