State Key Laboratory of Crop Stress Biology for Arid Areas/Shaanxi Key Laboratory of Apple, College of Horticulture, Northwest A&F University, Yangling 712100, China.
Plant Physiol. 2023 Jan 2;191(1):789-806. doi: 10.1093/plphys/kiac512.
Low temperature affects the yield and quality of crops. Inducer of CBF expression 1 (ICE1) plays a positive role in plant cold tolerance by promoting the expression of CRT binding factor (CBF) and cold-responsive (COR) genes. Several ICE1-interacting transcription factors (TFs) that regulate plant cold tolerance have been identified. However, how these TFs affect the function of ICE1 and CBF expression under cold conditions remains unclear. Here, we identified the MYC-type TF MdbHLH4, a negative regulator of cold tolerance in Arabidopsis (Arabidopsis thaliana) and apple (Malus domestica) plants. Under cold conditions, MdbHLH4 inhibits the expression of MdCBF1 and MdCBF3 by directly binding to their promoters. It also interacts with MdICE1L, a homolog of AtICE1 in apple, and inhibits the binding of MdICE1L to the promoters of MdCBF1/3 and thus their expression. We showed that MdCAX3L-2, a Ca2+/H+ exchanger (CAX) family gene that negatively regulates plant cold tolerance, is also a direct target of MdbHLH4. MdbHLH4 reduced apple cold tolerance by promoting MdCAX3L-2 expression. Moreover, overexpression of either MdCAX3L-2 or MdbHLH4 promoted the cold-induced ubiquitination and degradation of MdICE1L. Overall, our results reveal that MdbHLH4 negatively regulates plant cold tolerance by inhibiting MdCBF1/3 expression and MdICE1L promoter-binding activity, as well as by promoting MdCAX3L-2 expression and cold-induced MdICE1L degradation. These findings provide insights into the mechanisms by which ICE1-interacting TFs regulate CBF expression and ICE1 function and thus plant cold tolerance.
低温会影响作物的产量和质量。诱导型冷应答元件结合因子 1（ICE1）通过促进 CRT 结合因子（CBF）和冷响应（COR）基因的表达，在植物耐寒性中发挥积极作用。已经鉴定出几种 ICE1 相互作用的转录因子（TFs），它们可以调节植物的耐寒性。然而，这些 TFs 如何在低温条件下影响 ICE1 和 CBF 的表达功能仍不清楚。在这里，我们鉴定了 MYC 型 TF MdbHLH4，它是拟南芥（Arabidopsis thaliana）和苹果（Malus domestica）植物中冷耐性的负调控因子。在低温条件下，MdbHLH4 通过直接结合其启动子来抑制 MdCBF1 和 MdCBF3 的表达。它还与 MdICE1L 相互作用，MdICE1L 是苹果中 AtICE1 的同源物，抑制 MdICE1L 与 MdCBF1/3 启动子的结合及其表达。我们表明，负调控植物耐寒性的 Ca2+/H+交换器（CAX）家族基因 MdCAX3L-2 也是 MdbHLH4 的直接靶标。MdbHLH4 通过促进 MdCAX3L-2 的表达来降低苹果的耐寒性。此外，MdCAX3L-2 或 MdbHLH4 的过表达均促进了冷诱导的 MdICE1L 泛素化和降解。总体而言，我们的结果表明，MdbHLH4 通过抑制 MdCBF1/3 的表达和 MdICE1L 启动子结合活性，以及促进 MdCAX3L-2 的表达和冷诱导的 MdICE1L 降解，负调控植物的耐寒性。这些发现为 ICE1 相互作用的 TF 如何调节 CBF 表达和 ICE1 功能以及植物耐寒性提供了深入的了解。
