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

<b>Background:</b> 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 <i>DFR</i> gene family is lacking in <i>Lonicera japonica</i> Thunb. <b>Methods:</b> In the present study, based on genome and transcriptome data of <i>L. japonica</i>, the research identified six <i>LjDFR</i> gene family members throughout the entire genome. <b>Results:</b> The <i>LjDFR</i> genes were located on Chr.04 and Chr.09 and the full-length coding sequences of <i>LjDFR1</i>-<i>LjDFR6</i> 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 <i>LjDFR</i> genes with <i>Capsicum annuum</i> and <i>Camellia sinensis</i>. Promoter analysis linked <i>LjDFR</i> genes to light response, hormone signaling, and stress-responses. qRT-PCR analysis demonstrated tissue-specific and stage-specific expression patterns among <i>LjDFR</i> members. Notably, <i>LjDFR2</i> expression was significantly higher in the intensely pigmented tissues of <i>Lonicera japonica</i> Thunb. var. <i>chinensis</i> (Wats.) Bak. compared to <i>L</i>. <i>japonica</i>. Coupled with its phylogenetic proximity to the anthocyanin-related <i>CsDFRa</i> and <i>CaDFR5</i> genes, this suggests that <i>LjDFR2</i> may be positively correlated with anthocyanin accumulation. Additionally, the expression of <i>LjDFR2</i> and <i>LjDFR4</i> was markedly induced by both drought and salt stress, indicating their roles in abiotic stress responses. <b>Conclusions:</b> This research provides a foundation for further functional studies of <i>LjDFR</i> genes in anthocyanin biosynthesis and stress resistance and offers candidate genes for molecular breeding of <i>L</i>. <i>japonica</i>.