Root-Derived Trans-Zeatin-Type Cytokinins Increase Cold Tolerance in Rice Seedlings by Regulating Energy Metabolism.

Rice seedlings are highly sensitive to low-temperature stress. Cytokinins are important endogenous signalling molecules in plants and play a critical role in regulating stress responses. However, the mechanism by which cytokinins mediate cold stress responses in rice seedlings remains unclear. In this study, we employed cold-tolerant and cold-sensitive rice cultivars, cytokinin-defective mutants and exogenous cytokinin supplementation to elucidate the mechanisms underlying cytokinin-mediated chilling adaptation. First, we compared the transcriptomic and metabolomic profiles of a cold-tolerant cultivar (HY73) and a cold-sensitive cultivar (WFY286) under low-temperature treatment (11°C for 8 h). The results revealed that cytokinins, along with energy metabolic pathways such as glycolysis and the tricarboxylic acid cycle, are closely associated with cold tolerance in rice seedlings. Compared with WFY286, HY73 presented higher levels of root-derived trans-zeatin (tZ)-type cytokinins in leaves, increased energy metabolism, elevated ATP content and increased energy charge. Furthermore, the tZ-type cytokinins transport-deficient mutant abcg18 presented reduced cold tolerance, lower energy metabolic activity and decreased ATP and energy charge levels, indicating that the transport of tZ-type cytokinins is crucial for cold stress responses. Leaf spraying with tZ significantly improved the energy metabolism and cold tolerance of WFY286 and abcg18. Taken together, our findings suggest that root-derived tZ-type cytokinins enhance low-temperature adaptation in rice seedlings by promoting energy metabolism and maintaining cellular energy homoeostasis. This study provides a theoretical basis for improving cold resistance in rice through manipulation of cytokinin signalling pathways.