The MdICE1/MdFAMA-MdTYDC Transcriptional Module Confers Cold Tolerance by Regulating Dopamine Metabolism in Apple

Low temperature is a critical abiotic stress that imposes major constraints on the sustainable development of the fruit tree industry. Although exogenous dopamine has been shown to enhance cold tolerance in plants, its molecular mechanisms in apple (Malus domestica) remain poorly understood. In this study, we systematically investigated the role of dopamine in cold stress using exogenous dopamine application, overexpression (OE), and RNA interference (RNAi) of the MdTYDC (a key enzyme in dopamine biosynthesis). Our findings demonstrate that dopamine enhances cold resistance in apple through multiple mechanisms, including reducing reactive oxygen species accumulation, improving photosynthesis and stomatal function, promoting anthocyanin biosynthesis, and upregulating CBF genes. Molecular genetic analyses further revealed that MdICE1, a central transcriptional regulator, directly binds to cis-regulatory elements in the MdTYDC promoter, thereby activating its transcription. Notably, we identified another bHLH transcription factor, MdFAMA, which interacts with MdICE1 and facilitates its binding to the MdTYDC promoter. This interaction amplifies dopamine biosynthesis and strengthens cold resistance. Moreover, exogenous dopamine treatment synergistically induced MdICE1 and MdFAMA expression, forming a positive feedback loop. This feedback mechanism establishes a hierarchical amplification of signalling, further reinforcing tolerance to low temperatures. Collectively, this study elucidates, for the first time, the molecular framework through which the MdICE1/MdFAMA-MdTYDC regulatory module orchestrates dopamine-mediated cold tolerance in apple, providing novel insights into stress adaptation in perennial fruit crops.