Rapid actin turnover is essential for numerous actin-based processes. However, how it is precisely regulated remains poorly understood. Actin-interacting protein 1 (AIP1) has been shown to be an important factor by acting coordinately with actin-depolymerizing factor (ADF)/cofilin in promoting actin depolymerization, the rate-limiting factor in actin turnover. However, the molecular mechanism by which AIP1 promotes actin turnover remains largely unknown in plants. Here, we provide a demonstration that AIP1 promotes actin turnover, which is required for optimal growth of rice plants. Specific down-regulation of OsAIP1 increased the level of filamentous actin and reduced actin turnover, whereas over-expression of OsAIP1 induced fragmentation and depolymerization of actin filaments and enhanced actin turnover. In vitro biochemical characterization showed that, although OsAIP1 alone does not affect actin dynamics, it enhances ADF-mediated actin depolymerization. It also caps the filament barbed end in the presence of ADF, but the capping activity is not required for their coordinated action. Real-time visualization of single filament dynamics showed that OsAIP1 enhanced ADF-mediated severing and dissociation of pointed end subunits. Consistent with this, the filament severing frequency and subunit off-rate were enhanced in OsAIP1 over-expressors but decreased in RNAi protoplasts. Importantly, OsAIP1 acts coordinately with ADF and profilin to induce massive net actin depolymerization, indicating that AIP1 plays a major role in the turnover of actin, which is required to optimize F-actin levels in plants.

译文

:快速的肌动蛋白更新对于许多基于肌动蛋白的过程至关重要。但是,如何对其进行精确调节仍然知之甚少。肌动蛋白相互作用蛋白1(AIP1)通过与肌动蛋白解聚因子(ADF)/ cofilin协同作用来促进肌动蛋白解聚(肌动蛋白周转的限速因子),已被证明是一个重要因素。但是,在植物中,AIP1促进肌动蛋白更新的分子机制仍然是未知的。在这里,我们提供了一个证明AIP1促进肌动蛋白更新,这是水稻植物最佳生长所必需的。 OsAIP1的特定下调增加了丝状肌动蛋白的水平并减少了肌动蛋白的转换,而过表达的OsAIP1则诱导了肌动蛋白丝的断裂和解聚,并提高了肌动蛋白的转化率。体外生化特征表明,尽管仅OsAIP1不会影响肌动蛋白动力学,但它会增强ADF介导的肌动蛋白解聚作用。在存在ADF的情况下,它也可以盖住灯丝倒刺的末端,但是对于它们的协同作用,不需要盖盖活动。实时可视化的单丝动力学表明,OsAIP1增强了ADF介导的尖端亚基的切断和解离。与此相一致,OsAIP1过表达中的细丝切断频率和亚基解离速率增加,而RNAi原生质体中的减少。重要的是,OsAIP1与ADF和profilin协同作用,诱导大量的肌动蛋白净解聚,这表明AIP1在肌动蛋白周转中起主要作用,这是优化植物中F-肌动蛋白水平所必需的。

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