Department of Biological Sciences, Purdue University, West Lafayette, Indiana 47907-2064, USA.
Plant Cell. 2011 Oct;23(10):3711-26. doi: 10.1105/tpc.111.090670. Epub 2011 Oct 18.
Actin filament arrays are constantly remodeled as the needs of cells change as well as during responses to biotic and abiotic stimuli. Previous studies demonstrate that many single actin filaments in the cortical array of living Arabidopsis thaliana epidermal cells undergo stochastic dynamics, a combination of rapid growth balanced by disassembly from prolific severing activity. Filament turnover and dynamics are well understood from in vitro biochemical analyses and simple reconstituted systems. However, the identification in living cells of the molecular players involved in controlling actin dynamics awaits the use of model systems, especially ones where the power of genetics can be combined with imaging of individual actin filaments at high spatial and temporal resolution. Here, we test the hypothesis that actin depolymerizing factor (ADF)/cofilin contributes to stochastic filament severing and facilitates actin turnover. A knockout mutant for Arabidopsis ADF4 has longer hypocotyls and epidermal cells when compared with wild-type seedlings. This correlates with a change in actin filament architecture; cytoskeletal arrays in adf4 cells are significantly more bundled and less dense than in wild-type cells. Several parameters of single actin filament turnover are also altered. Notably, adf4 mutant cells have a 2.5-fold reduced severing frequency as well as significantly increased actin filament lengths and lifetimes. Thus, we provide evidence that ADF4 contributes to the stochastic dynamic turnover of actin filaments in plant cells.
肌动蛋白丝阵列会根据细胞需求的变化以及对生物和非生物刺激的反应不断进行重塑。先前的研究表明，活的拟南芥表皮细胞皮质阵列中的许多单个肌动蛋白丝经历随机动力学，这是快速生长与大量切割活性导致的组装之间的平衡组合。从体外生化分析和简单的重组系统中可以很好地理解丝的周转率和动力学。然而，在活细胞中鉴定参与控制肌动蛋白动力学的分子参与者还需要使用模型系统，特别是那些可以将遗传学的力量与单个肌动蛋白丝的高时空分辨率成像相结合的模型系统。在这里，我们测试了肌动蛋白解聚因子（ADF）/丝切蛋白有助于随机丝切割并促进肌动蛋白周转率的假设。与野生型幼苗相比，拟南芥 ADF4 的敲除突变体具有更长的下胚轴和表皮细胞。这与肌动蛋白丝结构的变化相关；ADF4 细胞中的细胞骨架阵列明显更束状且密度更低。单个肌动蛋白丝周转率的几个参数也发生了变化。值得注意的是，ADF4 突变体细胞的切割频率降低了 2.5 倍，肌动蛋白丝长度和寿命显著增加。因此，我们提供了证据表明 ADF4 有助于植物细胞中肌动蛋白丝的随机动态周转。
