Department of Biology, University of Washington, Seattle, Washington 98195-1800, USA.
Plant Physiol. 2012 Jan;158(1):273-82. doi: 10.1104/pp.111.187559. Epub 2011 Nov 18.
Multiple mechanisms have been described for coordination of responses to the plant hormones auxin and brassinosteroids (Zhang et al., 2009). One unexplained phenomenon is the reliance of the auxin transcriptional response on a functional brassinosteroid pathway. In this study, we used luciferase reporters to interrogate the promoter of SMALL AUXIN-UP RNA15 (SAUR15), a well-characterized auxin and brassinosteroid early response gene in Arabidopsis (Arabidopsis thaliana). After identifying a minimal region sufficient for auxin response, we targeted predicted cis-regulatory elements contained within this sequence and found a critical subset required for hormone response. Specifically, reporter sensitivity to auxin treatment required two elements: a Hormone Up at Dawn (HUD)-type E-box and an AuxRE-related TGTCT element. Reporter response to brassinosteroid treatment relied on the same two elements. Consistent with these findings, the transcription factors BRASSINOSTEROID INSENSITIVE1-EMS SUPPESSOR1 and MONOPTEROS (MP)/ AUXIN RESPONSE FACTOR5 (ARF5) showed enhanced binding to the critical promoter region containing these elements. Treatment with auxin or brassinosteroids could enhance binding of either transcription factor, and brassinosteroid enhancement of MP/ARF5 binding required an intact HUD element. Conservation of clustered HUD elements and AuxRE-related sequences in promoters of putative SAUR15 orthologs in a number of flowering plant species, in combination with evidence for statistically significant clustering of these elements across all Arabidopsis promoters, provided further evidence of the functional importance of coordinated transcription factor binding.
多种机制已被描述用于协调植物激素生长素和油菜素内酯（Brassinosteroids）的响应（Zhang 等人，2009）。一个未解释的现象是生长素转录响应依赖于功能性油菜素内酯途径。在这项研究中，我们使用荧光素酶报告基因来研究 SMALL AUXIN-UP RNA15（SAUR15）的启动子，SAUR15 是拟南芥中一个特征明显的生长素和油菜素内酯早期响应基因（Arabidopsis thaliana）。在确定了一个足以响应生长素的最小区域后，我们针对该序列内预测的顺式调控元件，并发现了一个对激素响应至关重要的亚群。具体而言，报告基因对生长素处理的敏感性需要两个元件：一种 Hormone Up at Dawn（HUD）-type E-box 和一个 AuxRE 相关的 TGTCT 元件。报告基因对油菜素内酯处理的反应依赖于相同的两个元件。这些发现与以下发现一致，转录因子 BRASSINOSTEROID INSENSITIVE1-EMS SUPPRESSOR1 和 MONOPTEROS（MP）/AUXIN RESPONSE FACTOR5（ARF5）显示出增强结合含有这些元件的关键启动子区域的能力。生长素或油菜素内酯处理可以增强这两种转录因子的结合，而油菜素内酯增强 MP/ARF5 结合需要一个完整的 HUD 元件。在许多开花植物物种的推定 SAUR15 同源物的启动子中，簇集的 HUD 元件和 AuxRE 相关序列的保守性，以及这些元件在所有拟南芥启动子中呈现出统计学上显著聚类的证据，进一步证明了协调转录因子结合的功能重要性。
