OsbZIP83-OsCOMT15 module confers melatonin-ameliorated cold tolerance in rice.

Cold stress is one of the most common abiotic stresses, and melatonin (Mel) is involved in the regulation of plant cold tolerance. However, the detailed mechanism underlying Mel-mediated cold tolerance remains largely unknown. Here, we reveal that caffeic acid O-methyltransferase 15 (OsCOMT15) is cold-responsive (COR) and acts as a key modulator of Mel biosynthesis to enhance rice cold tolerance at the seedling stage. We also discover that OsbZIP83, a bZIP transcription factor, serves as the direct regulator of OsCOMT15 to control its transcription. Knocking out OsbZIP83 or OsCOMT15 caused cold-hypersensitive phenotypes and significantly decreased melatonin contents upon cold stress, while their overexpressing lines exhibited the opposite effects to cold treatment. Further analysis elucidates that OsbZIP83 activates the expression of OsCOMT15 and two known COR genes, DEHYDRATION-RESPONSIVE ELEMENT BINDING FACTOR 1s (OsDREB1A and OsDREB1G). The results demonstrate the functionalities of the OsbZIP83-OsDREB1s/OsCOMT15 module in rice cold tolerance via orchestrating melatonin synthesis and cold response. Collectively, the findings shed new insights on how phytohormones respond to chilling factors and provide potential avenues and strategies guiding the engineering of health-benefiting and stress-tolerating crops.