Genome-Wide Identification of the DFR Gene Family in Lonicera japonica Thunb. and Response to Drought and Salt Stress

Background: Dihydroflavonol 4-reductase (DFR) is pivotal for anthocyanin biosynthesis and plays a crucial role in plant development and stress adaptation. However, a systematic characterization of the DFR gene family is lacking in Lonicera japonica Thunb. Methods: In the present study, based on genome and transcriptome data of L. japonica, the research identified six LjDFR gene family members throughout the entire genome. Results: The LjDFR genes were located on Chr.04 and Chr.09 and the full-length coding sequences of LjDFR1-LjDFR6 were cloned. Subcellular localization analysis showed that LjDFRs are primarily found at the cell membrane and in the nucleus. Phylogenetic analysis showed closer clustering of LjDFR genes with Capsicum annuum and Camellia sinensis. Promoter analysis linked LjDFR genes to light response, hormone signaling, and stress-responses. qRT-PCR analysis demonstrated tissue-specific and stage-specific expression patterns among LjDFR members. Notably, LjDFR2 expression was significantly higher in the intensely pigmented tissues of Lonicera japonica Thunb. var. chinensis (Wats.) Bak. compared to L. japonica. Coupled with its phylogenetic proximity to the anthocyanin-related CsDFRa and CaDFR5 genes, this suggests that LjDFR2 may be positively correlated with anthocyanin accumulation. Additionally, the expression of LjDFR2 and LjDFR4 was markedly induced by both drought and salt stress, indicating their roles in abiotic stress responses. Conclusions: This research provides a foundation for further functional studies of LjDFR genes in anthocyanin biosynthesis and stress resistance and offers candidate genes for molecular breeding of L. japonica.