Center for Signal Transduction and Metabolomics, Key Laboratory of Photosynthesis and Environmental Molecular Physiology, Institute of Botany, Chinese Academy of Sciences, Beijing 100093, China.
Plant Cell. 2010 Nov;22(11):3745-63. doi: 10.1105/tpc.110.080283. Epub 2010 Nov 23.
Actin cables in pollen tubes serve as molecular tracks for cytoplasmic streaming and organelle movement and are formed by actin bundling factors like villins and fimbrins. However, the precise mechanisms by which actin cables are generated and maintained remain largely unknown. Fimbrins comprise a family of five members in Arabidopsis thaliana. Here, we characterized a fimbrin isoform, Arabidopsis FIMBRIN5 (FIM5). Our results show that FIM5 is required for the organization of actin cytoskeleton in pollen grains and pollen tubes, and FIM5 loss-of-function associates with a delay of pollen germination and inhibition of pollen tube growth. FIM5 decorates actin filaments throughout pollen grains and tubes. Actin filaments become redistributed in fim5 pollen grains and disorganized in fim5 pollen tubes. Specifically, actin cables protrude into the extreme tips, and their longitudinal arrangement is disrupted in the shank of fim5 pollen tubes. Consequently, the pattern and velocity of cytoplasmic streaming were altered in fim5 pollen tubes. Additionally, loss of FIM5 function rendered pollen germination and tube growth hypersensitive to the actin-depolymerizing drug latrunculin B. In vitro biochemical analyses indicated that FIM5 exhibits actin bundling activity and stabilizes actin filaments. Thus, we propose that FIM5 regulates actin dynamics and organization during pollen germination and tube growth via stabilizing actin filaments and organizing them into higher-order structures.
花粉管中的肌动蛋白丝作为细胞质流动和细胞器运动的分子轨道，由肌动蛋白束形成因子如绒毛蛋白和 fimbrin 形成。然而，肌动蛋白丝的生成和维持的精确机制在很大程度上仍然未知。 fimbrin 在拟南芥中包含五个成员的家族。在这里，我们对一个 fimbrin 同工型，拟南芥 fimbrin5（FIM5）进行了表征。我们的结果表明，FIM5 是花粉粒和花粉管中肌动蛋白细胞骨架组织所必需的，FIM5 功能丧失与花粉萌发延迟和花粉管生长抑制有关。FIM5 装饰花粉粒和花粉管中的肌动蛋白丝。在 fim5 花粉粒中，肌动蛋白丝重新分布，在 fim5 花粉管中排列紊乱。具体来说，肌动蛋白丝突出到极端尖端，它们的纵向排列在 fim5 花粉管的柄部被打乱。因此，fim5 花粉管中细胞质流动的模式和速度发生了改变。此外，FIM5 功能的丧失使花粉萌发和管生长对肌动蛋白解聚药物 latrunculin B 更加敏感。体外生化分析表明，FIM5 表现出肌动蛋白束形成活性并稳定肌动蛋白丝。因此，我们提出 FIM5 通过稳定肌动蛋白丝并将其组织成更高阶的结构，调节花粉萌发和管生长过程中的肌动蛋白动力学和组织。
