The phytohormone abscisic acid (ABA) is involved in various plant processes. In response to drought stress, plants quickly accumulate ABA, but the regulatory mechanism of ABA accumulation is largely unknown, especially in woody plants. In this study, we report that MdMYB88 and MdMYB124 are myeloblastosis (MYB) transcription factors critical for ABA accumulation in apple trees (Malus x domestica) following drought, and this regulation is negatively controlled by ABA. MdMYB88 and MdMYB124 positively regulate leaf water transpiration, photosynthetic capacity, and stress endurance in apple trees under drought conditions. MdMYB88 and MdMYB124 regulate the expression of biosynthetic and catabolic genes of ABA, as well as drought- and ABA- responsive genes. MdMYB88 associates with promoter regions of the ABA biosynthetic gene 9-cis-epoxycarotenoid dioxygenase 3 (NCED3). Finally, expression of MdMYB88 and MdMYB124 is repressed by ABA. Our results identify a feedback regulation of MdMYB88 and MdMYB124 in modulating ABA homeostasis in apple trees.

中文翻译：

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脱落酸稳态是由MdMYB88和MdMYB124的反馈调节介导的

植物激素脱落酸（ABA）参与各种植物过程。响应干旱胁迫，植物迅速积累ABA，但是ABA积累的调节机制在很大程度上尚不清楚，尤其是在木本植物中。在这项研究中，我们报告说MdMYB88和MdMYB124是成纤维细胞（MYB）转录因子，对苹果树中的ABA积累至关重要（Malus x domestica）干旱之后，该调控受到ABA的负面控制。MdMYB88和MdMYB124积极调节干旱条件下苹果树的叶片水分蒸腾，光合能力和耐力。MdMYB88和MdMYB124调节ABA的生物合成和分解代谢基因以及干旱和ABA响应基因的表达。MdMYB88与ABA生物合成基因9-顺式-环氧类胡萝卜素双加氧酶3（NCED3）的启动子区域相关联。最后，ABA抑制MdMYB88和MdMYB124的表达。我们的结果确定了MdMYB88和MdMYB124在调节苹果树ABA稳态中的反馈调节。