Adaptive cold-environmental strategies of Lonicera caerulea: synergistic regulation of anthocyanin and iridoid pathways in cold tolerance and fruit ripening.

Understanding how plants adapt to extreme cold and ripen fruit is a key question in plant biology. Lonicera caerulea (blue honeysuckle), a cold-tolerant berry species native to the northern temperate zone, is valued as a 'noble fruit' for its rich nutrient profile and serves as an ideal model for studies due to its unique ability to thrive in low temperatures and ripen fruit during early spring. Here, we generated a chromosome-level genome assembly for wild L. caerulea from the Changbai Mountain region. We integrated it with transcriptomic and metabolomic analyses to explore its molecular cold adaptation mechanisms. We found that L. caerulea achieves cold tolerance and fruit ripening through dynamic regulation of two important metabolic pathways. Under cold stress, the LcODO1/LcMYB15-LcSLAS module promotes iridoid accumulation, while the LcbHLH62/LcMYB3R5-LcF3GT module enhances anthocyanin biosynthesis, jointly increasing plant cold resistance. During fruit maturation, metabolite profiles show dynamic reprogramming: anthocyanin levels rise in both pulp and peel, while the content of bitter iridoids markedly decreases in the pulp. This work provides a comprehensive genomic framework for understanding cold adaptation mechanisms, offering valuable gene resources and a theoretical foundation for improving cold resistance and fruit quality in breeding programs.