Unveiling the dual roles of LjTT8: Positive regulation of anthocyanin biosynthesis and abiotic stress responses in Lonicera japonica

Lonicera japonica is an important medicinal and edible plant. Transcription factors are crucial regulators of plant development, and their study has significant agricultural value. Here, we identified 103 bHLH transcription factors in L. japonica , including three members of subfamily IIIf; all these bHLH genes harbored various cis -regulatory elements associated with development and stress responses. Flower development- and color-specific bHLH expression patterns were detected in Lonicera , and a significant positive correlation was observed between LjTT8 (a IIIf member) expression and anthocyanin accumulation. Overexpressing LjTT8 in Arabidopsis tt8 mutant rescued the anthocyanin-deficient phenotype, and in tobacco led to anthocyanin accumulation and deep purple flowers, accompanied by the upregulation of anthocyanin biosynthesis structural genes and transporter encoding genes, such as CHS , F3′H and GST . Yeast one-hybrid and dual-luciferase assays confirmed that LjTT8 can directly bind to the promoter of structural genes to activate their transcriptional activities. Furthermore, overexpression of LjTT8 in Arabidopsis exhibited enhanced tolerance to drought and salt stresses, which was accompanied by elevated expression of structural genes ( CHS , CHI , F3H , F3′H , DFR and ANS ) and stress-responsive genes ( ABF3 , RD29A , RD29B , SOS1 , SOS2 and SOS3 ), as well as reduced levels of O 2 − and H 2 O 2 but higher activities of SOD, POD, and CAT in transgenic plants under stresses. These results together suggested that LjTT8 may enhance plant stress tolerance by regulating antioxidant enzyme production, and promoting protective compound biosynthesis like flavonoids. This study offers insights into the molecular functions of bHLH transcription factors in Lonicera , emphasizing their agricultural utility. • LjTT8 regulates anthocyanin biosynthesis by activating the promoter of enzymes. • LjTT8 overexpression rescued the anthocyanin-deficient phenotype in Arabidopsis . • LjTT8 overexpression induced deep purple pigmentation in tobacco flowers. • LjTT8 enhanced plant’s drought/salt tolerance by modulating antioxidant system.