Auxin regulates the transcription of auxin-responsive genes by the TIR1/AFBs-Aux/IAA-ARF signaling pathway, and in this way facilitates plant growth and development. However, rapid, nontranscriptional responses to auxin that cannot be explained by this pathway have been reported. In this review, we focus on several examples of rapid auxin responses: (1) the triggering of changes in plasma membrane potential in various plant species and tissues, (2) inhibition of root growth, which also correlates with membrane potential changes, cytosolic Ca²⁺ spikes, and a rise of apoplastic pH, (3) the influence on endomembrane trafficking of PIN proteins and other membrane cargoes, and (4) activation of ROPs (Rho of plants) and their downstream effectors such as the cytoskeleton or vesicle trafficking. In most cases, the signaling pathway triggering the response is poorly understood. A role for the TIR1/AFBs in rapid root growth regulation is emerging, as well as the involvement of transmembrane kinases (TMKs) in the activation of ROPs. We discuss similarities and differences among these rapid responses and focus on their physiological significance, which remains an enigma in most cases.

中文翻译：

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没有时间进行转录——植物中生长素的快速反应

生长素通过TIR1/AFBs-Aux/IAA-ARF信号通路调节生长素响应基因的转录，从而促进植物的生长和发育。然而，已经报道了无法用该途径解释的对生长素的快速非转录反应。在这篇综述中，我们重点关注生长素快速反应的几个例子：（1）触发各种植物物种和组织中质膜电位的变化，（2）抑制根部生长，这也与膜电位变化、细胞溶质 Ca2+ 相关。²⁺尖峰，以及质外体 pH 值的升高，(3) 对 PIN 蛋白和其他膜货物的内膜运输的影响，以及 (4) ROP（植物的 Rho）及其下游效应器（例如细胞骨架或囊泡运输）的激活。在大多数情况下，人们对触发反应的信号通路知之甚少。TIR1/AFB 在快速根生长调节中的作用正在显现，跨膜激酶 (TMK) 也参与 ROP 的激活。我们讨论这些快速反应之间的相似性和差异，并重点关注它们的生理意义，这在大多数情况下仍然是一个谜。