The ABI5 transcription factor, which is a core component of the ABA signaling pathway, affects various plant processes, including seed development and germination and responses to environmental cues. The knotted1-like homeobox (KNOX) transcription factor has crucial functions related to plant development, including the regulation of various hormones. In this study, an ABA-responsive KNOX gene, MdKNOX19, was identified in apple (Malus domestica). The overexpression of MdKNOX19 increased the ABA sensitivity of apple calli, resulting in a dramatic up-regulation in the transcription of the Arabidopsis ABI5-like MdABI5 gene. Additionally, MdKNOX19 overexpression in Micro-Tom adversely affected fruit size and seed yield as well as enhanced ABA sensitivity and up-regulated SlABI5 transcription during seed germination and early seedling development. An examination of MdKNOX19-overexpressing Arabidopsis plants also revealed severe defects in seed development and up-regulated expression of ABA-responsive genes. Furthermore, we further confirmed that MdKNOX19 binds directly to the MdABI5 promoter to activate expression. Our findings suggest MdKNOX19 is a positive regulator of ABI5 expression, and the conserved module MdKNOX19-MdABI5-ABA may contribute to organ development.

中文翻译：

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MdKNOX19 是苹果的 II 类打结样转录因子，在器官发育过程中通过靶向 ABI5 在 ABA 信号传导/敏感性中发挥作用

ABI5 转录因子是 ABA 信号通路的核心成分，影响各种植物过程，包括种子发育和萌发以及对环境信号的反应。knotted1 样同源框 (KNOX) 转录因子具有与植物发育相关的关键功能，包括调节各种激素。在这项研究中，在苹果 (Malusdomestica) 中发现了一种 ABA 响应性 KNOX 基因 MdKNOX19。MdKNOX19 的过表达增加了苹果愈伤组织的 ABA 敏感性，导致拟南芥 ABI5 样 MdABI5 基因的转录显着上调。此外，MdKNOX19 在 Micro-Tom 中的过表达对果实大小和种子产量产生不利影响，并在种子萌发和幼苗早期发育过程中增强了 ABA 敏感性并上调了 SlABI5 转录。对过表达 MdKNOX19 的拟南芥植物的检查也揭示了种子发育的严重缺陷和 ABA 响应基因的上调表达。此外，我们进一步证实 MdKNOX19 直接与 MdABI5 启动子结合以激活表达。我们的研究结果表明 MdKNOX19 是 ABI5 表达的正调节因子，保守模块 MdKNOX19-MdABI5-ABA 可能有助于器官发育。