Kinesin-4 Functions in Vesicular Transport on Cortical Microtubules and Regulates Cell Wall Mechanics during Cell Elongation in Plants.

This is the accepted manuscript. The final version is available at http://www.cell.com/molecular-plant/abstract/S1674-2052%2815%2900091-X.In plants, anisotropic cell expansion depends on cortical microtubules that serve as tracks along which macromolecules and vesicles are transported by the motor kinesins of unknown identities. We used cotton (Gossypium hirsutum) fibers that underwent robust elongation to discover kinesins that are involved in cell elongation and found Gh KINESIN-4A expressed abundantly. The motor was detected by immunofluorescence on vesicle-like structures that were associated with cortical microtubules. In Arabidopsis thaliana, the orthologous motor At KINESIN-4A/FRA1, previously implicated in cellulose deposition during secondary growth in fiber cells, was examined by live-cell imaging in cells expressing the fluorescently tagged functional protein. The motor decorated vesicle-like particles that exhibit a linear movement along cortical microtubules with an average velocity of 0.89 μm/min, which was significantly different from those linked to cellulose biosynthesis. We also discovered that At KINESIN-4A/FRA1 and the related At KINESIN-4C play redundant roles in cell wall mechanics, cell elongation, and the axial growth of various vegetative and reproductive organs, as the loss of At KINESIN-4C greatly enhanced the defects caused by a null mutation at the KINESIN-4A/FRA1 locus. The double mutant displayed a lack of cell wall softening at normal stages of rapid cell elongation. Furthermore, enhanced deposition of arabinose-containing carbohydrate was detected in the kinesin-4 mutants. Our findings established a connection between the Kinesin-4-based transport of cargoes containing non-cellulosic components along cortical microtubules and cell wall mechanics and cell elongation in flowering plants.This report is based on work supported by the National Science Foundation under grant MCB-1243959 (BL and YRJL), Physical Biosciences Program of the Office of Basic Energy Sciences of the U.S. Department of Energy under the contracts DE-FG02-04ER15554 (BL) and DEFG02- 03ER15415 (Z-HY). SL is supported by the Center for LignoCellulose Structure and Formation, an Energy Frontier Research Center funded by the U.S. Department of Energy under the award DE-SC0001090 and SAB is supported by a Gatsby Foundation Fellowship

The γ -Tubulin Complex Protein GCP4 Is Required for Organizing Functional Microtubule Arrays in Arabidopsis thaliana[W]

This study demonstrates that γ -Tubulin Complex Protein 4 plays a crucial role in γ -tubulin–mediated microtubule nucleation and organization during cell division and morphogenesis in Arabidopsis

Synthesis of (<i>Z</i>)‑1-Thio- and (<i>Z</i>)‑2-Thio-1-alkenyl Boronates via Copper-Catalyzed Regiodivergent Hydroboration of Thioacetylenes: An Experimental and Theoretical Study

A Cu-catalyzed divergent hydroboration of thioacetylenes has been achieved, providing (<i>Z</i>)-1-thio- or (<i>Z</i>)-2-thio-1-alkenyl boronates in moderate to high yields with excellent regio- and stereoselectivity, by using pinacolborane or bis­(pinacolato)­diboron as the hydroborating reagents, respectively. DFT calculations indicate that the sulfur atom plays a key role in determining the regioselectivity through polarizing the C–C triple bonds and participating in the HOMO orbitals. Moreover, the SR group can serve as a good leaving group, resulting in the concise synthesis of six regio- and stereoisomers of trisubstituted alkenes <b>5</b> via the iterative cross-coupling of C–B and C–S bonds. Clearly, it will be valuable for assembling stereochemically diverse trisubstituted olefins in organic synthesis

Augmin triggers microtubule-dependent microtubule nucleation in interphase plant cells.

Microtubule (MT)-dependent MT nucleation by γ-tubulin is required for interphase plant cells to establish a highly dynamic cortical MT network underneath the plasma membrane, which influences the deposition of cell wall materials and consequently governs patterns of directional cell expansion. Newly formed MTs either assume 40° angles or are parallel to the extant ones. To date, it has been enigmatic how the γ-tubulin complex is recruited to the sidewall of cortical MTs and initiates MT nucleation. Here, we discovered that the augmin complex was recruited to cortical MTs and initiated MT nucleation in both branching and parallel forms. The augmin complex overwhelmingly colocalized with the γ-tubulin complex. When the function of the augmin complex was compromised, MT nucleation frequency was drastically reduced, most obviously for the branching nucleation. Consequently, the augmin knockdown cells displayed highly parallel and bundled MTs, replacing the fine and mesh-like MT network in the wild-type cells. Our findings uncovered a mechanism by which the augmin complex functions in recruiting the γ-tubulin complex to cortical MTs and initiating MT nucleation, and they shifted the paradigm of the commonly perceived mitotic-specific function of augmin and established its crucial function in MT-dependent MT nucleation in interphase plant cells

Augmin triggers microtubule-dependent microtubule nucleation in interphase plant cells.

Microtubule (MT)-dependent MT nucleation by γ-tubulin is required for interphase plant cells to establish a highly dynamic cortical MT network underneath the plasma membrane, which influences the deposition of cell wall materials and consequently governs patterns of directional cell expansion. Newly formed MTs either assume 40° angles or are parallel to the extant ones. To date, it has been enigmatic how the γ-tubulin complex is recruited to the sidewall of cortical MTs and initiates MT nucleation. Here, we discovered that the augmin complex was recruited to cortical MTs and initiated MT nucleation in both branching and parallel forms. The augmin complex overwhelmingly colocalized with the γ-tubulin complex. When the function of the augmin complex was compromised, MT nucleation frequency was drastically reduced, most obviously for the branching nucleation. Consequently, the augmin knockdown cells displayed highly parallel and bundled MTs, replacing the fine and mesh-like MT network in the wild-type cells. Our findings uncovered a mechanism by which the augmin complex functions in recruiting the γ-tubulin complex to cortical MTs and initiating MT nucleation, and they shifted the paradigm of the commonly perceived mitotic-specific function of augmin and established its crucial function in MT-dependent MT nucleation in interphase plant cells

Augmin Plays a Critical Role in Organizing the Spindle and Phragmoplast Microtubule Arrays in Arabidopsis[W]

Two augmin complex proteins, which play a critical role in microtubule organization in the spindle and phragmoplast during cell division of plant cells, are identified in this study