MOE Key Laboratory of Cell Activities and Stress Adaptations, School of Life Sciences, Lanzhou University, Lanzhou 730000, China.
State Key Laboratory of Plant Physiology and Biochemistry, Department of Plant Sciences, College of Biological Sciences, China Agricultural University, Beijing 100193, China.
Mol Plant. 2017 Aug 7;10(8):1065-1081. doi: 10.1016/j.molp.2017.06.001. Epub 2017 Jun 9.
Dynamics of the actin cytoskeleton are essential for pollen germination and pollen tube growth. ACTIN-DEPOLYMERIZING FACTORs (ADFs) typically contribute to actin turnover by severing/depolymerizing actin filaments. Recently, we demonstrated that Arabidopsis subclass III ADFs (ADF5 and ADF9) evolved F-actin-bundling function from conserved F-actin-depolymerizing function. However, little is known about the physiological function, the evolutional significance, and the actin-bundling mechanism of these neofunctionalized ADFs. Here, we report that loss of ADF5 function caused delayed pollen germination, retarded pollen tube growth, and increased sensitive to latrunculin B (LatB) treatment by affecting the generation and maintenance of actin bundles. Examination of actin filament dynamics in living cells revealed that the bundling frequency was significantly decreased in adf5 pollen tubes, consistent with its biochemical functions. Further biochemical and genetic complementation analyses demonstrated that both the N- and C-terminal actin-binding domains of ADF5 are required for its physiological and biochemical functions. Interestingly, while both are atypical actin-bundling ADFs, ADF5, but not ADF9, plays an important role in mature pollen physiological activities. Taken together, our results suggest that ADF5 has evolved the function of bundling actin filaments and plays an important role in the formation, organization, and maintenance of actin bundles during pollen germination and pollen tube growth.
肌动蛋白细胞骨架的动态变化对于花粉萌发和花粉管生长至关重要。肌动蛋白解聚因子（ADFs）通常通过切断/解聚肌动蛋白丝来促进肌动蛋白的周转。最近，我们证明了拟南芥 III 类 ADF（ADF5 和 ADF9）通过保守的 F-肌动蛋白解聚功能进化出了 F-肌动蛋白成束功能。然而，对于这些新功能化的 ADF 的生理功能、进化意义和肌动蛋白成束机制，人们知之甚少。在这里，我们报告说，ADF5 功能的丧失通过影响肌动蛋白束的产生和维持，导致花粉萌发延迟、花粉管生长缓慢以及对拉曲库林 B（LatB）处理更加敏感。对活细胞中肌动蛋白丝动力学的研究表明，在 adf5 花粉管中，成束频率显著降低，与它的生化功能一致。进一步的生化和遗传互补分析表明，ADF5 的 N-和 C-末端肌动蛋白结合结构域都对其生理和生化功能是必需的。有趣的是，尽管 ADF5 和 ADF9 都是非典型的肌动蛋白成束 ADF，但 ADF5 在成熟花粉的生理活动中起着重要作用，而不是 ADF9。总之，我们的研究结果表明，ADF5 已经进化出了成束肌动蛋白丝的功能，并在花粉萌发和花粉管生长过程中，对于肌动蛋白束的形成、组织和维持起着重要作用。
