Mechanism of CAP1-mediated apical actin polymerization in pollen tubes
Mechanism of CAP1-mediated apical actin polymerization in pollen tubes
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CAP1介导的花粉管顶端肌动蛋白聚合机制
DOI：
10.1073/pnas.1821639116
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发表时间：
2019-06-11
影响因子：
11.1
通讯作者：
Huang, Shanjin
中科院分区：
文献类型：
--
作者：
Jiang, Yuxiang;Chang, Ming;Huang, Shanjin
意义 肌动蛋白聚合驱动快速极化花粉管生长，但花粉管生长域内肌动蛋白聚合的机制仍不完全清楚。我们在此确定CAP1是通过给ADP-G-肌动蛋白充电来驱动肌动蛋白聚合的主要参与者，并以涉及花粉管中CAP1的核苷酸交换活性的方式促进具有聚合能力的肌动蛋白单体池的形成和维持。我们的研究将 CAP1 的肌动蛋白核苷酸交换活性与其促进肌动蛋白聚合的作用直接联系起来。因此，我们的研究显着增强了我们对花粉管中肌动蛋白聚合机制的理解。 Srv2p/CAP1 是肌动蛋白周转的重要调节因子，但其在调节肌动蛋白聚合中的确切功能，特别是其肌动蛋白核苷酸交换活性的贡献，仍不完全清楚。我们发现，虽然拟南芥CAP1均匀分布在细胞质中，但其功能丧失对花粉管不同区域内的肌动蛋白细胞骨架有不同的影响。具体而言，cap1 花粉管柄中的 F-肌动蛋白水平增加，但顶端区域的 F-肌动蛋白水平降低。顶端 F-肌动蛋白的减少主要是由于 cap1 花粉管内膜源肌动蛋白聚合受损所致。 CAP1 的肌动蛋白核苷酸交换活性参与顶端肌动蛋白聚合。 CAP1在体外与花粉ADF和profilin协同促进肌动蛋白转换，并且可以克服ADF的抑制作用并与profilin协同促进肌动蛋白核苷酸交换。与其作为 ADF 和 profilin 之间穿梭分子的作用一致，CAP1 的胞质浓度远低于花粉中 ADF 和 profilin 的浓度。因此，CAP1与ADF和profilin协同作用，驱动花粉中的肌动蛋白周转，并以涉及其肌动蛋白核苷酸交换活性的方式促进花粉管中的顶端肌动蛋白聚合。
Significance Actin polymerization drives rapid polarized pollen tube growth, but the mechanism underlying actin polymerization within the growth domain of pollen tubes remains incompletely understood. We here identify CAP1 as a major player in driving actin polymerization via recharging ADP-G-actin and facilitating the formation and maintenance of a pool of polymerization-competent actin monomers in a manner that involves the nucleotide exchange activity of CAP1 in pollen tubes. Our study directly links the actin nucleotide exchange activity of CAP1 to its role in promoting actin polymerization. Our study thus significantly enhances our understanding of the mechanism of actin polymerization in pollen tubes. Srv2p/CAP1 is an essential regulator of actin turnover, but its exact function in regulating actin polymerization, particularly the contribution of its actin nucleotide exchange activity, remains incompletely understood. We found that, although Arabidopsis CAP1 is distributed uniformly in the cytoplasm, its loss of function has differential effects on the actin cytoskeleton within different regions of the pollen tube. Specifically, the F-actin level increases in the shank but decreases in the apical region of cap1 pollen tubes. The reduction in apical F-actin results mainly from impaired polymerization of membrane-originated actin within cap1 pollen tubes. The actin nucleotide exchange activity of CAP1 is involved in apical actin polymerization. CAP1 acts synergistically with pollen ADF and profilin to promote actin turnover in vitro, and it can overcome the inhibitory effects of ADF and synergize with profilin to promote actin nucleotide exchange. Consistent with its role as a shuttle molecule between ADF and profilin, the cytosolic concentration of CAP1 is much lower than that of ADF and profilin in pollen. Thus, CAP1 synergizes with ADF and profilin to drive actin turnover in pollen and promote apical actin polymerization in pollen tubes in a manner that involves its actin nucleotide exchange activity.