Abstract：
B-Box-containing zinc finger transcription factors (BBX) are involved in light-mediated growth, affecting processes such as hypocotyl elongation in Arabidopsis thaliana. However, the molecular and hormonal framework that regulates plant growth through BBX proteins is incomplete. Here, we demonstrate that BBX21 inhibits the hypocotyl elongation through the brassinosteroid (BR) pathway. BBX21 reduces the sensitivity to 24-epiBL, a synthetic active BR, principally at very-low concentrations in simulated shade. The biosynthesis profile of BRs showed that two active BR -brassinolide (BL) and 28-homobrassinolide (28-homoBL)- and 8 of 11 intermediates can be repressed by BBX21 under white light (WL) or simulated shade. Furthermore, BBX21 represses the expression of CYTOCHROME P450 90B1 (DWF4/CYP90B1), BRASSINOSTEROID-6-OXIDASE 1 (BR6OX1, CYP85A1) and BR6OX2 (CYP85A2) genes involved in the BR biosynthesis in WL while specifically promoting DWF4 and PHYB ACTIVATION TAGGED SUPPRESSOR 1 (CYP2B1/BAS1) expression in WL supplemented with far-red (WL+FR), a treatment that simulates shade. In addition, BBX21 represses BR signalling genes such as PACLOBUTRAZOL RESISTANCE1 (PRE1), PRE3 and ARABIDOPSIS MYB-LIKE 2 (MYBL2), and auxin-related and expansin genes, such as INDOLE-3-ACETIC ACID INDUCIBLE 1 (IAA1), IAA4 and EXPANSIN 11 (EXP11) in short-term shade. By a genetic approach we found that BBX21 acts genetically upstream of BRASSINAZOLE-RESISTANT 1 (BZR1) for the promotion of DWF4 and BAS1 gene expression in shade. We propose that BBX21 integrates the BR homeostasis and shade-light signalling allowing the fine-tuning of hypocotyl elongation in Arabidopsis.
摘要：
含B盒的锌指转录因子（BBX）参与光介导的生长，影响拟南芥下胚轴伸长等过程。然而,通过BBX蛋白调节植物生长的分子和激素框架是不完整的。这里,我们证明BBX21通过油菜素类固醇（BR）途径抑制下胚轴伸长。BBX21降低了对24-epiBL的敏感性，合成活性BR，主要在模拟阴影中浓度非常低。BRs的生物合成谱表明，在白光（WL）或模拟阴影下，BBX21可以抑制两种活性BR-油菜素内酯（BL）和28-高油菜素内酯（28-homoBL）-以及11种中间体中的8种。此外，BBX21抑制细胞色素P45090B1（DWF4/CYP90B1）的表达，在补充远红（WL+FR）的WL中，参与BR生物合成的Brassinostoid-6-oxidase1（BR6OX1，CYP85A1）和BR6OX2（CYP85A2）基因特异性促进DWF4和PHYB激活标记的抑制1（CYP2B1/BAS1）表达，一种模拟阴凉处的治疗方法.此外,BBX21抑制BR信号基因，如帕洛布特拉唑抗性1(PRE1)，PRE3和ARABIDOPSISMYB样2（MYBL2），和生长素相关基因和expansin基因，如吲哚-3-乙酸诱导剂1(IAA1)，IAA4和EXPANSIN11（EXP11）短期阴影。通过遗传方法，我们发现BBX21在雷公藤酮抗性1（BZR1）的基因上游起作用，以促进阴影中DWF4和BAS1基因的表达。我们建议BBX21整合BR稳态和阴影光信号，从而可以微调拟南芥的下胚轴伸长。
