Overexpression of an Arabidopsis formin stimulates supernumerary actin cable formation from pollen tube cell membrane
Overexpression of an Arabidopsis formin stimulates supernumerary actin cable formation from pollen tube cell membrane
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DOI：
10.1105/tpc.016550
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发表时间：
2004-01-01
期刊：
影响因子：
11.6
通讯作者：
Wu, HM
中科院分区：
文献类型：
--
作者：
Cheung, AY;Wu, HM
Formins，肌动蛋白成核蛋白，刺激肌动蛋白丝的重新聚合，对多种细胞和发育过程，特别是那些依赖于极性建立的过程非常重要。植物formins的一个子集，称为第1组，与其他物种的formins不同，它们进化出独特的n端结构，具有信号肽，富含pro的潜在糖基化的细胞外结构域和跨膜结构域。我们在这里表明，拟南芥花粉管中过表达AFH1诱导肌动蛋白电缆阵列的形成，这些电缆从细胞膜投射到细胞质中，其n端结构将AFH1靶向细胞膜。花粉管伸长是一个极细胞生长过程，依赖于活跃和严格调控的肌动蛋白细胞骨架。在转化的花粉管中，AFH1的轻微表达促进了花粉管的生长，但其过表达会导致花粉管增宽、生长去极化和生长停滞。这些结果表明，afh1调控的肌动蛋白聚合在极花粉细胞生长过程中起重要作用。此外，在尖端膨大、过表达afh1的花粉管的顶端区域，观察到严重的膜变形，其中afh1诱导的膜相关肌动蛋白索丰富。这些观察结果表明，细胞表面AFH1活性的调节对于维持花粉管极性延伸的尖端聚焦细胞膜扩张是重要的。位于细胞表面的i族形成蛋白可能作为肌动蛋白细胞骨架外部刺激的介质发挥着类似于整合素的作用，而AFH1可能在传粉过程中介导来自雌性组织的细胞外信号以引起适当的花粉管生长反应中发挥重要作用。
Formins, actin-nucleating proteins that stimulate the de novo polymerization of actin filaments, are important for diverse cellular and developmental processes, especially those dependent on polarity establishment. A subset of plant formins, referred to as group 1, is distinct from formins from other species in having evolved a unique N-terminal structure with a signal peptide, a Pro-rich, potentially glycosylated extracellular domain, and a transmembrane domain. We show here that overexpression of the Arabidopsis formin AFH1 in pollen tubes induces the formation of arrays of actin cables that project into the cytoplasm from the cell membrane and that its N-terminal structure targets AFH1 to the cell membrane. Pollen tube elongation is a polar cell growth process dependent on an active and tightly regulated actin cytoskeleton. Slight increases in AFH1 stimulate growth, but its overexpression induces tube broadening, growth depolarization, and growth arrest in transformed pollen tubes. These results suggest that AFH1-regulated actin polymerization is important for the polar pollen cell growth process. Moreover, severe membrane deformation was observed in the apical region of tip-expanded, AFH1-overexpressing pollen tubes in which an abundance of AFH1-induced membrane-associated actin cables was evident. These observations suggest that regulated AFH1 activity at the cell surface is important for maintaining tip-focused cell membrane expansion for the polar extension of pollen tubes. The cell surface-located group-I formins may play the integrin-analogous role as mediators of external stimuli to the actin cytoskeleton, and AFH1 could be important for mediating extracellular signals from female tissues to elicit the proper pollen tube growth response during pollination.