State Key Laboratory of Crop Stress Biology for Arid Areas/Shaanxi Key Laboratory of Apple, College of Horticulture, Northwest A&F University, Yangling, Shaanxi 712100, China.
State Key Laboratory of Crop Stress Biology for Arid Areas, College of Plant Protection, Northwest A&F University, Yangling, Shaanxi 712100, China.
Plant Physiol. 2021 Apr 23;185(4):1903-1923. doi: 10.1093/plphys/kiaa116.
The R2R3 transcription factor MdMYB88 has previously been reported to function in biotic and abiotic stress responses. Here, we identify BRI1 ETHYLMETHANE SULFONATE SUPRESSOR1 (MdBES1), a vital component of brassinosteroid (BR) signaling in apple (Malus × domestica) that directly binds to the MdMYB88 promoter, regulating the expression of MdMYB88 in a dynamic and multifaceted mode. MdBES1 positively regulated expression of MdMYB88 under cold stress and pathogen attack, but negatively regulated its expression under control and drought conditions. Consistently, MdBES1 was a positive regulator for cold tolerance and disease resistance in apple, but a negative regulator for drought tolerance. In addition, MdMYB88 participated in BR biosynthesis by directly regulating the BR biosynthetic genes DE ETIOLATED 2 (MdDET2), DWARF 4 (MdDWF4), and BRASSINOSTEROID 6 OXIDASE 2 (MdBR6OX2). Applying exogenous BR partially rescued the erect leaf and dwarf phenotypes, as well as defects in stress tolerance in MdMYB88/124 RNAi plants. Moreover, knockdown of MdMYB88 in MdBES1 overexpression (OE) plants decreased resistance to a pathogen and C-REPEAT BINDING FACTOR1 expression, whereas overexpressing MdMYB88 in MdBES1 OE plants increased expression of SQUAMOSA PROMOTER BINDING PROTEIN-LIKE 3 （MdSPL3） and BR biosynthetic genes, suggesting that MdMYB88 contributes to MdBES1 function during BR biosynthesis and the stress response. Taken together, our results reveal multifaceted regulation of MdBES1 on MdMYB88 in BR biosynthesis and stress tolerance.
先前有报道称 R2R3 转录因子 MdMYB88 参与了生物和非生物胁迫反应。在这里，我们鉴定了一个苹果（Malus × domestica）中至关重要的油菜素内酯（BR）信号组分 BRI1 ETHYLMETHANE SULFONATE SUPRESSOR1（MdBES1），它直接与 MdMYB88 启动子结合，以动态和多方面的方式调节 MdMYB88 的表达。MdBES1 正向调控冷胁迫和病原菌攻击下 MdMYB88 的表达，但负调控对照和干旱条件下其表达。一致地，MdBES1 是苹果耐寒性和抗病性的正调控因子，但耐旱性的负调控因子。此外，MdMYB88 通过直接调控 BR 生物合成基因 DE ETIOLATED 2（MdDET2）、DWARF 4（MdDWF4）和 BRASSINOSTEROID 6 OXIDASE 2（MdBR6OX2）参与 BR 生物合成。施加外源 BR 部分挽救了 MdMYB88/124 RNAi 植物的直立叶和矮化表型以及对胁迫的耐受性缺陷。此外，在 MdBES1 过表达（OE）植物中敲低 MdMYB88 降低了对病原体的抗性和 C-REPEAT BINDING FACTOR1 的表达，而在 MdBES1 OE 植物中过表达 MdMYB88 增加了 SQUAMOSA PROMOTER BINDING PROTEIN-LIKE 3（MdSPL3）和 BR 生物合成基因的表达，表明 MdMYB88 在 BR 生物合成和胁迫反应中有助于 MdBES1 发挥功能。总之，我们的研究结果揭示了 MdBES1 对 MdMYB88 在 BR 生物合成和胁迫耐受性中的多方面调控。
