背景回顾：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. 

提出问题：However, how these TFs affect the function of ICE1 and CBF expression under cold conditions remains unclear. 

主要发现：Here, we identified the MYC-type TF MdbHLH4, a negative regulator of cold tolerance in Arabidopsis (Arabidopsis thaliana) and apple (Malus domestica) plants. 

结果1-bHLH4抑制CBF1/3的表达、促进ICE1的结合活性：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. 

结果2-bHLH4促进CAX3L的表达：We showed that MdCAX3L-2, a CAX (Ca2+/H+ exchanger) 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. 

结果3-bHLH4促进ICE1的降解：Moreover, overexpression of either MdCAX3L-2 or MdbHLH4 promoted the cold-induced ubiquitination and degradation of MdICE1L. 

结论：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.

 摘 要 

低温影响作物的产量和质量。ICE1通过促进CBF和COR基因的表达，在植物耐寒性中发挥正调控作用。目前，已经鉴定了一些ICE1互作的转录因子，可以介导植物的低温耐受性调控。然而，这些转录因子如何在低温条件下影响ICE1的功能以及CBF的表达，这些问题尚不清楚。本文中，作者鉴定到了一个转录因子MdbHLH4，作为拟南芥和苹果中的低温耐受性负调控因子发挥功能。在低温条件下，MdbHLH4通过直接结合MdCBF1/3基因的启动子来抑制这两个基因的的表达。MdbHLH4还能够苹果中AtICE1的同源物MdICE1L互作，并抑制其结合MdCBF1/3基因启动子的能力，从而间接抑制MdCBF1/3基因的表达。作者发现一个负调控植物低温耐受性的CAX基因家族成员MdCAX3L-2，也是MdbHLH4的直接靶基因。MdbHLH4通过促进MdCAX3L-2基因的表达，降低苹果的低温耐受性。此外，无论是过表达MdCAX3L-2还是MdbHLH4，均会促进MdICE1L蛋白受低温诱导的泛素化和降解。综上，本文的研究结果表明，MdbHLH4通过抑制MdCBF1/3基因的表达和MdICE1L启动子结合活性，同时促进MdCAX3L-2基因的表达和低温诱导的MdICE1L降解，从而负调控植物的低温耐受性。这些发现为ICE1互作转录因子调节CBF基因表达和ICE1功能，从而调控植物低温耐受性的分子机制提供了新的见解。

** 马锋旺 **