Arabidopsis basic leucine Zipper transcription factors function as quantitative modulators of auxin mediated transcription
Arabidopsis basic leucine Zipper transcription factors function as quantitative modulators of auxin mediated transcription
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DOI：
10.53846/goediss-1478
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发表时间：
2012-04
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影响因子：
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通讯作者：
C. Weiste
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作者：
C. Weiste
植物生长素是植物生长过程中的一种重要激素，它参与了植物生长过程中的一系列发育和环境过程。一般来说，这些反应主要通过生长素反应基因的编码活性来实现，这些基因受到生长素反应因子（ARF）家族和AUX/IAA蛋白类的共同调节。而ARF转录因子（TF）发挥其反式激活特性后，直接结合到它们的同源生长素反应元件（AUXINREs），AUX/IAA转录阻遏物接触ARF蛋白质，以调节其活性。为了维持植物的最佳生长，生长素介导的反应必须根据主要的内源和环境条件进行调节。因此，需要将相应的刺激整合到生长素相关的转录模式中。生物信息学启动子顺式元件分析表明，生长素反应基因的启动子不仅富含GREs，而且富含G-BOX相关元件（GREs）和MYB反应元件（MREs）。使用拟南芥AtGH3.3启动子作为生长素响应模型系统，通过这些部分冗余作用的顺式元件的复杂排列组合控制生长素介导的转录已被证明。AuxRE作为生长素依赖性开关发挥作用，而GRE和MRE作为定量调节剂发挥作用。在原生质体中应用反式激活筛选方法，已经鉴定了碱性亮氨酸拉链（bZIP）TF的C/S1网络的成员，其通过结合GRE顺式元件来增强和敏化生长素介导的转录。在转基因植物中的互补、获得和丧失功能的方法证实，密切相关的组S1 AtbZIP 2、-11和-44 TF调节生长素诱导的转录，并且能够改变典型的生长素相关的生长反应，如主根生长、侧根形成、根毛密度和向地性。生长素响应DR 5：GFP报告基因的组织化学表达分析表明生长素分布和/或信号传导中的bZIP依赖性改变。随后对S1 bZIPs组对生长素介导的转录的机制作用的研究揭示，特别是AtbZIP 11相关的TF能够通过其N-末端激活结构域募集SAGA样乙酰化机制。药理学和反向遗传学方法清楚地定义了组蛋白乙酰化在生长素诱导的转录中的影响。事实上，染色质免疫沉淀（ChIP）分析证实了组蛋白乙酰化机制和RNA聚合酶II的bZIP依赖性募集。总之，这些数据表明一种新的bZIP介导的机制，微调染色质的可及性在生长素诱导的基因激活。由于C/S1 bZIP-TF在能量应激时重新编程初级代谢，GRE/bZIP模块可能起到“变阻器”的作用
The essential plant growth hormone auxin orchestrates a wide range of developmental and environmental processes in the course of plant life. In general, these responses are predominately implemented by the encoded activity of auxin responsive genes, which are corporately regulated by the family of Auxin Response Factors (ARFs) and the class of AUX/IAA proteins. Whereas ARF transcription factors (TFs) exert their trans-activating properties upon direct binding to their cognate Auxin Response Elements (AuxREs), the AUX/IAA transcriptional repressors contact the ARF proteins to modulate their activity. In order to sustain optimal plant growth, auxin mediated responses have to be adjusted according to the prevailing endogenous and environmental conditions. Thus an integration of the corresponding stimuli into auxin-related transcriptional patterns is required. Bioinformatic promoter cis-element analyses revealed that promoters of auxin responsive genes are not only significantlyenriched for AuxREs, but also for the G-BOX RELATED ELEMENTS (GREs) and MYB RESPONSIVE ELEMENTS (MREs). Using the Arabidopsis AtGH3.3 promoter as an auxin responsive model system, a combinatorial control of auxin-mediated transcription by a complex arrangement of these, in part redundantly acting, cis-elements has been demonstrated. Whereas AuxREs function as auxin-dependent switches, GREs and MREs act as quantitative modulators. Applying a trans-activation screening approach in protoplasts, members of the C/S1 network of basic leucine zipper (bZIP) TFs have been identified, which enhance and sensitize auxin-mediated transcription via binding the GRE cis-element. Complementary, gain- and loss-of-function approaches in transgenic plants confirm that the closely related group S1 AtbZIP2, -11 and -44 TFs modulate auxin-induced transcription and are capable to alter typical auxin-related growth-responses, such as primary root growth, lateral root formation, root hair density and gravitropism. Histochemical expression analysis of the auxin respon sive DR5:GFP reporter suggests bZIP-dependent alterations in auxin distribution and/or signalling. Ensuing studies on the mechanistical action of the group S1 bZIPs on auxin mediated transcription revealed that particularly AtbZIP11-related TFs are able to recruit the SAGA-like acetylation machinery via their N-terminal activation domain. Pharmacological and reverse genetic approaches clearly define the impact of histone acetylation in auxin-induced transcription. In fact, Chromatin-Immunoprecipitation (ChIP) analyses confirm bZIP-dependent recruitment of the histone acetylation machinery and RNA-Polymerase II. Altogether, these data suggest a novel bZIP-mediated mechanism to fine-tune chromatin accessibility during auxin-induced gene activation. As C/S1 bZIP-TFs are reprogramming the primary metabolism in response to energy stress, the GRE/bZIP module might function as a “rheostat