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[交流] [优秀文章推荐]厦大揭示生长素合成酶基因TAA1的转录调控机制

      该研究证明细胞分裂素B类ARRs在激素，环境以及发育信号对TAA1的转录调控中扮演着核心的角色。

      TAA1（拟南芥色氨酸氨基转移酶1）催化由色氨酸形成吲哚3丙酮酸的反应。该反应是IPA所依赖的生长素合成通路中的第一步。TAA1的表达呈组织特异性，其表达受发育信号、植物激素和外界环境因子的调控，但是其调控机制目前并不清楚。本研究对TAA1的转录调控机制进行了探索，发现TAA1启动子和第二个内含子中包含两个调控TAA1组织特异性的表达所必须的顺式调控元件。部分细胞分裂素B类ARRs（Arabidopsis Response Regulators）的C末端（如ARR1C）可以直接特异性地结合到上述顺式调控元件，并激活其下游报告基因的表达。B类ARRs是细胞分裂素信号转导途径中的重要组分。进一步研究则表明B类ARRs不仅介导了细胞分裂素对于TAA1的转录调控中，也参与到了乙烯和光信号对TAA1的表达调控。介导赤霉素和乙烯信号转导的DELLA和EIN3-GFP转录因子可直接与ARR1C相互作用并促进ARR1C的转录活性。由此，我们提出细胞分裂素B类ARRs是TAA1转录调控的核心组分，整合了激素，环境以及发育信号对TAA1的调控。

A proposed model showing that the type B ARRs function as central transcriptional regulators of TAA1.

      生长素是调控植物生长发育的重要植物激素。在调控植物胚胎发育、器官形成以及植物的向性反应等生理过程中，生长素通过建立合适的浓度梯度行使其功能，而这种浓度梯度的建立则依赖于植物对生长素合成与代谢以及转运过程的有序调节来实现的。许多生长素合成基因的表达均存在组织特异性，并且受到外界环境信号的调节。我们的研究拓展了我们有关植物生长素合成基因的调控机制的认识。

      During embryogenesis and organ formation, establishing proper gradient is critical for auxin function, which is achieved through coordinated regulation of both auxin metabolism and transport. Expression of auxin biosynthetic genes is often tissue specific and is regulated by environmental signals. However, the underlying regulatory mechanisms remain elusive. Here, we investigated the transcriptional regulation of a key auxin biosynthetic gene, TAA1 (L-Tryptophan aminotransferase of Arabidopsis 1). A canonical and a novel ARR (Arabidopsis response regulators) binding site were identified in the promoter and the second intron of TAA1, which were required for its tissue specific expression. C-terminals of a subset of the type B ARRs selectively bind to one or both cis-elements and activate the expression of TAA1. We further demonstrated that the ARRs not only mediate the transcriptional regulation of TAA1 by cytokinins, but also mediate its regulation by ethylene, light and developmental signals. Through direct protein-protein interactions，the transcriptional activity of ARR1 is enhanced by ARR12, DELLAs and EIN3. Our study thus revealed the ARR proteins act as key node that mediate the regulation of auxin biosynthesis by various hormonal, environmental and developmental signals through transcriptional regulation of the key auxin biosynthesis gene TAA1.

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