Actin binding proteins and transcription factors are essential in regulating plant root hair growth in response to various environmental stresses; however, the interaction between these two factors in regulating root hair growth remains poorly understood. Apical and subapical thick actin bundles are necessary for terminating rapid elongation of root hair cells. Here, we show that Arabidopsis (Arabidopsis thaliana) actin-bundling protein Villin1 (VLN1) decorates filaments in shank, subapical, and apical hairs. vln1 mutants displayed significantly longer hairs with longer hair growing time and defects in the thick actin bundles and bundling activities in the subapical and apical regions, whereas seedlings overexpressing VLN1 showed different results. Genetic analysis showed that the transcription factor GLABRA2 (Gl2) played a regulatory role similar to that of VLN1 in hair growth and actin dynamics. Moreover, further analyses demonstrated that VLN1 overexpression suppresses the gl2 mutant phenotypes regarding hair growth and actin dynamics; GL2 directly recognizes the promoter of VLN1 and positively regulates VLN1 expression in root hairs; and the GL2-mediated VLN1 pathway is involved in the root hair growth response to osmotic stress. Our results demonstrate that the GL2-mediated VLN1 pathway plays an important role in the root hair growth response to osmotic stress, and they describe a transcriptional mechanism that regulates actin dynamics and thereby modulates cell tip growth in response to environmental signals.

肌动蛋白结合蛋白和转录因子对于调节植物根毛生长以应对各种环境胁迫至关重要；然而，这两个因素在调节根毛生长方面的相互作用仍然知之甚少。顶端和顶端下的厚肌动蛋白束对于终止根毛细胞的快速伸长是必需的。在这里，我们展示了拟南芥 ( Arabidopsis thaliana ) 肌动蛋白捆绑蛋白 Villin1 (VLN1) 装饰着柄毛、顶端毛和顶端毛中的细丝。 vln1突变体表现出明显更长的毛发和更长的毛发生长时间，以及根尖下和根尖区域的粗肌动蛋白束和成束活性缺陷，而过表达VLN1的幼苗则表现出不同的结果。遗传分析表明，转录因子 GLABRA2 (Gl2) 在毛发生长和肌动蛋白动力学中发挥与 VLN1 类似的调节作用。此外，进一步的分析表明， VLN1过表达会抑制与毛发生长和肌动蛋白动力学有关的gl2突变体表型； GL2直接识别VLN1的启动子并正向调节根毛中VLN1的表达； GL2介导的VLN1途径参与根毛生长对渗透胁迫的反应。我们的结果表明，GL2 介导的 VLN1 通路在根毛生长对渗透胁迫的反应中发挥着重要作用，并且它们描述了调节肌动蛋白动力学的转录机制，从而响应环境信号调节细胞尖端的生长。