番茄侧枝发生激素调控网络中油菜素内酯的作用及机制

Plant lateral bud outgrowth is controlled by an interconnected hormone network including auxin, strigolactone (SL) and cytokinin (CTK). We found that endogenous brassinosteroid (BR) positively regulated lateral bud outgrowth in tomato, indicating that BR may be another hormone governing lateral bud outgrowth. Therefore, it is necessary to study the relationship among BR, auxin, SL and CTK in lateral bud outgrowth, and unravel the molecular mechanism of BR action. The proposal mainly uses BR biosynthetic gene deficient mutant and overexpressing transgenic tomato plants to study the regulation of SL biosynthesis by BR through its interaction with auxin for lateral bud outgrowth regulation, study the regulation of CTK biosynthesis by BR and dissect the role of the regulation in lateral bud outgrowth in tomato. Based on these studies, the proposal will study the regulation of BRC1 by downstream BR signaling transcription factor BES1, and uncover the role of the regulation in lateral bud outgrowth. In addition, the proposal will identify the BES1-regulated genes and uncover the role of the genes in lateral bud outgrowth. The execution of the proposal will elucidate the mechanism of BR regulation of lateral bud outgrowth, and help to provide theoretic basis for improving plant architecture in tomato.

已有的研究发现生长素、独角金内酯（SL）和细胞分裂素（CTK）是调控植物侧芽生长的重要激素。我们发现，番茄体内油菜素内酯（BR）的含量与侧芽的发生呈正相关。因此，BR可能是调控植物侧芽生长的另一重要激素，有必要探讨BR与已知分枝调控激素的互作关系，并解析BR调控番茄侧芽生长的分子机制。申请项目主要以番茄BR合成基因缺失突变体和过量表达转基因植株为材料，研究BR调控番茄侧芽生长中与生长素和SL的关系，明确BR通过CTK对侧芽生长直接的调控作用；在此基础上进一步揭示BR信号转导下游转录因子BES1对分枝关键基因BRC1表达的调控在番茄侧芽生长中的作用，并挖掘BES1调控基因阐明其功能。项目的实施有助于阐明BR调控番茄侧芽生长的机制，并为改善番茄株型这一重要农艺性状提供理论依据。

植物顶端优势的调控涉及生长素、独脚金内酯（SLs）、细胞分裂素（CKs）和糖，但对该调控网络的具体作用机制尚不完全清楚。通过项目研究，我们明确了油菜素内酯（BR）通过BR信号关键转录因子BRASSINAZOLE-RESISTANT1（BZR1）直接转录调控BRANCHED1（BRC1）基因来促进番茄的侧芽生长。去顶、生长素或SLs合成的抑制、CK和蔗糖处理能显著抑制BRC1基因表达并促进侧芽生长，但这些作用在BR缺陷型或bzr1突变体中显著减弱。此外，去顶、生长素或SLs合成的抑制、CK和蔗糖处理显著促进侧芽中BR含量和去磷酸化形式BZR1的积累。另一方面，生长素和SLs抑制CK积累，而蔗糖处理增加CK积累。 CK通过B型响应因子RR10直接调控BR合成基因DWF表达进而促进侧芽中BR积累。我们的结果表明，BR信号整合了控制侧枝发生的多种途径。侧芽中局部BR信号的调控是塑造植物株型的有效靶标。

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