Genome-wide identification of the CjCCO family in Japanese cedar, and CjCCD4a and CjCCD4d confer stress tolerance in transgenic Arabidopsis

Carotenoid cleavage oxidases (CCOs) are crucial for plant growth and stress responses, whereas the CCO gene family in Cryptomeria japonica remains unreported. Here, we identified 18 CjCCO genes from its whole genome and analysed their sequence characteristics, phylogenetic relationships, interaction networks and functional enrichment pathways. Furthermore, the key genes, CjCCD4a and CjCCD4d, identified through comparative transcriptomics, were subjected to gene expression analyses, yeast self-activation assays and functional studies. The CjCCOs encoded proteins spanning 492–854 amino acids, and were categorized into five subgroups: CjCCD1s, CjCCD4s, CjCCD7s, CjCCD8s and CjNCEDs. Genes within each subfamily displayed conserved gene structures and motifs. Functional enrichment analysis revealed their involvement in various biochemical processes, and cis-acting element predictions indicated associations with light signaling, hormone regulation, environmental stress responses, and growth and development. CjCCD4a and CjCCD4d transgenic Arabidopsis exhibited reduced chlorophyll degradation and malondialdehyde accumulation, and increased photosynthetic capacity, antioxidant enzyme activity and abscisic acid content, compared with wild-type, thereby enhancing plant stress resistance. This study provides comprehensive insights into the CjCCO gene family, laying a valuable foundation for further functional investigations.