MdSCL13 coordinates with MdTCP2 to positively regulate cold tolerance by mediating ROS scavenging and JA biosynthesis

The SCL13 is a Scarecrow-like (SCL) protein. However, whether and how it plays a functional role under cold stress in apple remains largely unclear. In this study, we demonstrate that MdSCL13 responds to cold and plays a positive role in regulating apple cold tolerance. RNA-seq and RT-qPCR analyses revealed that MdSCL13 regulates the expression of genes associated with cold response, reactive oxygen species (ROS) detoxification, and jasmonic acid (JA) biosynthesis. In addition, the apple transcription factor TEOSINTE BRANCHED 1/CYCLOIDEA/PROLIFERATING CELL FACTOR, MdTCP2, a positive regulator of cold stress, interacts with MdSCL13. The MdSCL13-MdTCP2 complex substantially upregulates MdAOC4 and MdGSTU8 expression during cold stress, with MdTCP2 mediating this effect by specifically binding to the GGGACC and GGGTCC motifs in their promoters, respectively. Collectively, our findings show that MdSCL13 interacts with MdTCP2 to form a functional complex that enhances cold tolerance in apple by promoting ROS scavenging and JA accumulation. This study reveals a novel mechanism whereby a GRAS protein integrates hormonal biosynthesis and redox homeostasis to confer cold tolerance in apple.