Cai Chao, Henty-Ridilla Jessica L, Szymanski Daniel B, Staiger Christopher J
Department of Biological Sciences (C.C., J.L.H.-R., C.J.S.), Center for the Direct Catalytic Conversion of Biomass to Biofuels (C.C., J.L.H.-R., D.B.S., C.J.S.), and Department of Agronomy (D.B.S.), Purdue University, West Lafayette, Indiana 47907.
Department of Biological Sciences (C.C., J.L.H.-R., C.J.S.), Center for the Direct Catalytic Conversion of Biomass to Biofuels (C.C., J.L.H.-R., D.B.S., C.J.S.), and Department of Agronomy (D.B.S.), Purdue University, West Lafayette, Indiana 47907
Plant Physiol. 2014 Nov;166(3):1359-70. doi: 10.1104/pp.114.244335. Epub 2014 Sep 18.
Plant cell expansion relies on intracellular trafficking of vesicles and macromolecules, which requires myosin motors and a dynamic actin network. Arabidopsis (Arabidopsis thaliana) myosin XI powers the motility of diverse cellular organelles, including endoplasmic reticulum, Golgi, endomembrane vesicles, peroxisomes, and mitochondria. Several recent studies show that there are changes in actin organization and dynamics in myosin xi mutants, indicating that motors influence the molecular tracks they use for transport. However, the mechanism by which actin organization and dynamics are regulated by myosin XI awaits further detailed investigation. Here, using high spatiotemporal imaging of living cells, we quantitatively assessed the architecture and dynamic behavior of cortical actin arrays in a mutant with three Myosin XI (XI-1, XI-2, and XI-K) genes knocked out (xi3KO). In addition to apparent reduction of organ and cell size, the mutant showed less dense and more bundled actin filament arrays in epidermal cells. Furthermore, the overall actin dynamicity was significantly inhibited in the xi3KO mutant. Because cytoskeletal remodeling is contributed mainly by filament assembly/disassembly and translocation/buckling, we also examined the dynamic behavior of individual actin filaments. We found that the xi3KO mutant had significantly decreased actin turnover, with a 2-fold reduction in filament severing frequency. Moreover, quantitative analysis of filament shape change over time revealed that myosin XI generates the force for buckling and straightening of both single actin filaments and actin bundles. Thus, our data provide genetic evidence that three Arabidopsis class XI myosins contribute to actin remodeling by stimulating turnover and generating the force for filament shape change.
植物细胞扩张依赖于囊泡和大分子的细胞内运输，这需要肌球蛋白马达和动态的肌动蛋白网络。拟南芥的肌球蛋白XI驱动包括内质网、高尔基体、内膜囊泡、过氧化物酶体和线粒体在内的多种细胞器的运动。最近的几项研究表明，肌球蛋白xi突变体中肌动蛋白的组织和动力学发生了变化，这表明马达会影响它们用于运输的分子轨道。然而，肌球蛋白XI调节肌动蛋白组织和动力学的机制仍有待进一步详细研究。在这里，我们利用活细胞的高时空成像技术，定量评估了一个敲除了三个肌球蛋白XI（XI-1、XI-2和XI-K）基因（xi3KO）的突变体中皮质肌动蛋白阵列的结构和动态行为。除了器官和细胞大小明显减小外，该突变体在表皮细胞中还表现出密度较低且更成束的肌动蛋白丝阵列。此外，xi3KO突变体中整体肌动蛋白的动态性受到显著抑制。由于细胞骨架重塑主要由丝状体的组装/拆卸以及易位/弯曲引起，我们还研究了单个肌动蛋白丝的动态行为。我们发现，xi3KO突变体的肌动蛋白周转显著降低，丝状体切断频率降低了2倍。此外，对丝状体形状随时间变化的定量分析表明，肌球蛋白XI产生了单根肌动蛋白丝和肌动蛋白束弯曲和伸直的力。因此，我们的数据提供了遗传学证据，表明拟南芥的三个XI类肌球蛋白通过刺激周转和产生丝状体形状变化的力来促进肌动蛋白重塑。
