Genome-Wide Identification, Cloning and Expression Analysis of <em>DFR</em> Gene Family in <em>Lonicera japonica</em> Thunb. under Drought and Salt Stress

Based on the genome and transcriptome data of Lonicera japonica Thunb., this study identified six LjDFR gene family members at the genome-wide level. These genes were located on Chr.04 and Chr.09, and the full-length coding sequences of LjDFR1 to LjDFR6 were successfully cloned. The proteins encoded by the cloned genes are all hydrophilic, with secondary structures dominated by α-helices and random coils. The subcellular localization analysis indicated that LjDFRs are primarily localized in the cell membrane and nucleus. Phylogenetic analysis classified the LjDFR proteins into four subfamilies, clustering with DFR homologs from species such as Capsicum annuum and Camellia sinensis, reflecting a high degree of evolutionary conservation. Promoter analysis identified multiple cis-acting elements associated with light response, hormone signaling, and stress-responses. Expression pattern analysis demonstrated that LjDFR genes exhibit tissue-specific and stage-specific expression patterns during flower development in L. japonica varieties with different floral colors. Notably, LjDFR2 expression was significantly higher in the deeply pigmented tissues of Lonicera japonica Thunb. var. chinensis (Wats.) Bak. than in L. japonica. Together with its phylogenetic clustering with the anthocyanin-related CsDFRa and CaDFR5 genes, this finding suggests that LjDFR2 potentially positively correlated with anthocyanin accumulation. Furthermore, the expression of LjDFR2 and LjDFR4 was significantly induced under both drought and salt stress, indicating their involvement in abiotic stress responses. This study provides a foundation for further functional characterization of LjDFR genes in anthocyanin metabolism and stress resistance, and offers valuable candidate genes for molecular breeding of L. japonica.