Auxin plays a central role in controlling plant cell growth and morphogenesis. Application of auxin to light-grown seedlings elicits both axial growth and transverse patterning of the cortical microtubule cytoskeleton in hypocotyl cells. Microtubules respond to exogenous auxin within 5 min, although repatterning of the array does not initiate until 30 min after application and is complete by 2 h. To examine the requirements for auxin-induced microtubule array patterning, we used an Arabidopsis (Arabidopsis thaliana) double auxin f-box (afb) receptor mutant, afb4-8 afb5-5, that responds to conventional auxin (indole-3-acetic acid) but has a strongly diminished response to the auxin analog, picloram. We show that 5 µm picloram induces immediate changes to microtubule density and later transverse microtubule patterning in wild-type plants, but does not cause microtubule array reorganization in the afb4-8 afb5-5 mutant. Additionally, a dominant mutant (axr2-1) for the auxin coreceptor AUXIN RESPONSIVE2 (AXR2) was strongly suppressed for auxin-induced microtubule array reorganization, providing additional evidence that auxin functions through a transcriptional pathway for transverse patterning. We observed that brassinosteroid application mimicked the auxin response, showing both early and late microtubule array effects, and induced transverse patterning in the axr2-1 mutant. Application of auxin to the brassinosteroid synthesis mutant, diminuto1, induced transverse array patterning but did not produce significant axial growth. Thus, exogenous auxin induces transverse microtubule patterning through the TRANSPORT INHIBITOR 1/AUXIN F-BOX (TIR1/AFB) transcriptional pathway and can act independently of brassinosteroids.

中文翻译：

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外源生长素通过运输抑制剂/ AUXIN信号传递F-BOX受体诱导横向微管阵列。

生长素在控制植物细胞生长和形态发生中起重要作用。在生长较轻的幼苗上应用生长素会引起下胚轴细胞中皮质微管细胞骨架的轴向生长和横向模式。微管对外源生长素的反应在5分钟内完成，尽管阵列的重新分散直到应用后30分钟才开始，并在2小时内完成。为了检查对植物生长素诱导的微管阵列模式的要求，我们使用了拟南芥（Arabidopsis thaliana）双生长素f-box（afb）受体突变体afb4-8 afb5-5，它对常规的生长素（吲哚-3-乙酸）有反应），但对生长素类似物Picloram的反应却大大减弱。我们发现5 µm吡咯仑会引起野生型植物中微管密度的立即变化，以及随后的横向微管构图，但不会在afb4-8，afb5-5突变体中引起微管阵列重组。此外，对于生长素诱导的微管阵列重组，强烈抑制了生长素共受体AUXIN RESPONSIVE2（AXR2）的显性突变体（axr2-1），提供了其他证据表明生长素通过转录途径进行横向构图。我们观察到油菜素类固醇的应用模仿了生长素的反应，显示出早期和晚期的微管阵列效应，并在axr2-1突变体中诱导了横向模式。将生长素应用于油菜素类固醇合成突变体diminuto1，可诱导横向阵列构图，但不会产生明显的轴向生长。因此，