Genome-wide identification of the aldo-keto reductase gene family and functional characterization of CsAKRIVB2 conferring cold tolerance in tea plant (Camellia sinensis).

Aldo-keto reductases (AKRs) are a superfamily of NADPH-dependent oxidoreductases that play a crucial role in detoxifying reactive carbonyl species and maintaining redox homeostasis under abiotic stresses. However, systematic characterization of AKRs and their functional roles in cold stress responses in tea plants (Camellia sinensis) remain largely unexplored. We identified 48 CsAKR genes genome-wide and classified them into four groups. Structural and promoter analyses pointed to conserved protein backbones alongside diversified regulatory architectures. Expression profiling and RT-qPCR screening identified CsAKRIVB2 as a cold-inducible candidate, which contains seven ARE motifs, the highest counts in the family. The protein localized to both the nucleus and cytoplasm. CsAKRIVB2 overexpression consistently enhanced cold tolerance in E. coli, N. benthamiana, and transgenic Arabidopsis. Transgenic OE lines exhibited lower ROS and MDA levels, higher SOD/POD/CAT activities, and sustained expression of multiple cold-responsive genes, including COR15A, COR15B, RD29A, KIN1, and SnRK2.4, alongside upregulated antioxidant genes such as CAT1, APX2, FSD1, MDAR1, and GR2, under cold stress. These results demonstrate that CsAKRIVB2 functions as a positive regulator of cold tolerance and represents a promising candidate for breeding cold-tolerant tea varieties.