独脚金内酯信号途径的新发现——抑制子也是转录因子

doi:10.11983/CBB20099

摘要/Abstract

摘要： 植物激素信号传导途径中的抑制子(repressor) DELLA、AUX/IAA、JAZ和D53/SMXL均结合下游转录因子并抑制其转录活性, 从而阻遏激素响应基因的表达; 激素分子则激活信号传导链降解抑制子、释放转录因子, 从而诱导响应基因表达并介导相应的生物学功能。中国科学院遗传与发育生物学研究所李家洋研究团队最新的研究发现, 独脚金内酯(SL)信号途径中的SMXL6、SMXL7和SMXL8是具有抑制子和转录因子双重功能的新型抑制子, 他们还通过研究SL转录调控网络发现了大量新的SL响应基因, 揭示了SL调控植物分枝、叶片伸长和花色素苷积累的分子机制。这些重要发现为探索植物激素作用机理提供了新思路, 具有重要科学意义和应用前景。

关键词: 植物激素, 独脚金内酯, 抑制子, 转录因子, 双重功能, 负反馈调节

Abstract: It is well-known that DELLA, AUX/IAA, JAZ and D53/SMXL act as repressor proteins that bind and repress transcription factors to suppress expression of hormone-responsive genes, while hormone molecules trigger signal transduction to induce degradation of these repressor proteins and eventually activate expression of hormone-responsive genes essential for various biological processes. The research team led by Dr. Jiayang Li recently reported that SMXL6, SMXL7 and SMXL8 (SMXL6,7,8) in strigolactone (SL) signaling pathway serve as dual-function repressor proteins which act as both repressors and transcription factors. They found that SMXL6,7,8 can function as transcription factors by directly binding to the promoters of SMXL6,7,8 genes and repressing their expression. In addition, they identified a large number of novel SL-responsive genes, and revealed molecular mechanisms underlying how SL regulates shoot branching, leaf elongation and anthocyanin biosynthesis. These important findings provide new insights into our understanding of plant hormone action, which are scientifically significant and agriculturally important.

Key words: phytohormone, strigolactone, repressor, transcription factor, dual functions, negative feedback regulation

姚瑞枫,谢道昕. 独脚金内酯信号途径的新发现——抑制子也是转录因子. 植物学报, 2020, 55(4): 397-402.

Ruifeng Yao,Daoxin Xie. New Insight into Strigolactone Signaling. Chinese Bulletin of Botany, 2020, 55(4): 397-402.

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链接本文: https://www.chinbullbotany.com/CN/10.11983/CBB20099

https://www.chinbullbotany.com/CN/Y2020/V55/I4/397

图/表 2

图1 独脚金内酯信号通路中抑制子SMXL6,7,8的双重功能工作模型独脚金内酯信号通路中的SMXL6,7,8是具有双重功能的新型抑制子: SMXL6,7,8作为抑制子招募TPL共抑制子并直接结合下游转录因子抑制其转录活性, 从而阻遏独脚金内酯(SL)响应基因的表达; 同时SMXL6,7,8又作为转录因子直接结合并抑制SMXL6,7,8基因的启动子。SL被D14感知, 诱导SMXL6,7, 8-D14-MAX2复合体形成, 导致SMXL6,7,8通过泛素化-蛋白酶体途径降解, 从而解除SMXL6,7,8对下游转录因子以及自身基因启动子的抑制, 一方面激活BRC1、TCP1和PAP1等响应基因的转录, 最终调控植物分枝、叶片伸长和花色素苷积累等生物学过程; 另一方面解除对SMXL6,7,8启动子的抑制, 激活SMXL6,7,8自身基因的表达, 形成维持SL通路稳态的负反馈调控体系。SCF: Skp1-Cullin-F-box; UB: 泛素

Figure 1 Working model for the dual-function repressors SMXL6,7,8 in strigolactone signaling SMXL6,7,8 in the strigolactone signaling pathway act as novel repressors with dual functions: SMXL6,7,8 act as repressors that recruit TPL co-repressor proteins and bind transcription factors to inhibit their transcriptional activity, thereby suppressing expression of strigolactone (SL)-responsive genes; meanwhile, SMXL6,7,8 also serve as transcription factors that directly bind and inhibit the promoters of SMXL6,7,8 genes. SL is perceived by D14 to trigger formation of SMXL6,7,8-D14-MAX2 complex and further induce SMXL6,7,8 degradation via the ubiquitination-proteasome pathway. The SL-induced SMXL6,7,8 degradation releases transcription factors to activate expression of the SL-responsive genes such as BRC1, TCP1 and PAP1 essential for plant branching, leaf elongation, and anthocyanin biosynthesis, respectively. Such SMXL6,7,8 degradation also de- represses the SMXL6,7,8 suppression on the SMXL6,7,8 promoters to activate the expression of SMXL6,7,8 genes, which forms a negative feedback regulation loop that maintains the homeostasis of SL pathway. SCF: Skp1-Cullin-F- box; UB: Ubiquitin

图2 独脚金内酯、赤霉素、茉莉素及生长素信号途径中抑制子的功能比较植物激素独脚金内酯(A)、赤霉素(B)、茉莉素(C)及生长素(D)信号传导途径中的抑制子DELLA、AUX/IAA、JAZ和D53/SMXL均通过结合下游信号蛋白(转录因子)调控其转录活性, 从而阻遏激素响应基因的表达。激素分子被相应的受体识别后激活其信号传导链,诱导抑制子通过泛素化-蛋白酶体途径降解, 促进响应基因表达并介导相应的生物学功能。独脚金内酯(SL)信号传导途径中的抑制子SMXL6,7,8同时还作为转录因子直接结合并抑制SMXL6,7,8基因的启动子; SL诱导SMXL6,7,8降解, 从而解除SMXL6,7,8对自身基因启动子的抑制, 激活SMXL6,7,8自身基因的表达, 形成维持SL通路稳态的负反馈调控体系(A)。

Figure 2 Comparison of the repressor proteins in strigolactone, gibberellin, jasmonate and auxin signaling pathways The repressor proteins D53/SMXL, DELLA, JAZ, and AUX/IAA in the signaling pathways of strigolactone (A), gibberellin (B), jasmonate (C) and auxin (D) bind and inhibit downstream transcription factors, thereby suppressing the expression of hormone-responsive genes. Hormone molecule is recognized by corresponding receptor protein and activates the signal transduction chain to induce the degradation of the repressor protein via ubiquitination-proteasome pathway, then triggering response gene expression and related biological processes. Moreover, the repressor proteins SMXL6,7,8 in strigolactone (SL) signaling pathway can also directly bind and inhibit the promoter of SMXL6,7,8 gene as transcription factors. SL induces the degradation of SMXL6,7,8 to release its repression on the SMXL6,7,8 promoters to activate the expression of SMXL6,7,8 genes, forming a negative feedback regulation loop (A) essential for the homeostasis of SL pathway.

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