The regulatory cascade CtrMYC2-CtrMYB20-CtrSTP13 boosts sugar and JA accumulation for cold tolerance in Citrus

Jasmonic acid (JA) and soluble sugars are known to play critical roles in modulating cold tolerance in plants. However, the interplay between these signaling and metabolic pathways, as well as the transcriptional networks involved, remains poorly understood. In this study, we demonstrated that JA signaling was required for cold tolerance and for the cold-induced accumulation of soluble sugars in Citrus trifoliata. Integrated analyses of MeJA- and cold-treated transcriptomes identified CtrSTP13 as the most strongly induced sugar transporter gene under both conditions. CtrSTP13, localized to the plasma membrane and highly expressed in leaves, functioned as a hexose transporter for enhancing sugar accumulation and cold tolerance. We further revealed that the transcription factor CtrMYB20 was a direct positive regulator of CtrSTP13 expression, thereby controlling cold tolerance in a CtrSTP13-dependent manner. Additionally, CtrMYC2 acted as an upstream transcriptional activator of CtrMYB20 and positively regulated cold tolerance by indirectly promoting CtrSTP13-mediated sugar accumulation. Notably, overexpression of CtrSTP13 led to increased α-linolenic acid levels and upregulation of the JA biosynthetic gene CtrLOX3, and stimulated JA biosynthesis, whereas silencing CtrSTP13 produced opposite effects. Interestingly, knockdown of CtrLOX3 disrupted sugar-induced JA accumulation and impaired cold tolerance. Collectively, our results demonstrate that JA promotes cold-induced sugar accumulation through the transcriptional cascade CtrMYC2-CtrMYB20-CtrSTP13, while sugars feedback to enhance CtrLOX3-mediated JA biosynthesis, thereby establishing a regulatory loop that facilitates cold adaptation. These findings provide new insights into the elucidation of integrated JA signaling and sugar metabolism associated with plant cold stress responses.