BackgroundThe homeodomain-leucine zipper I (HD-Zip I) transcription factor is a plant-specific protein that plays an essential role in the abiotic stress response of plants. Research on the HD-Zip I family inSalvia miltiorrhizais still lacking.Methods and ResultsIn this study, a total of 25 SmHD-Zip I proteins were identified. Their characterizations, phylogenetic relationships, conserved motifs, gene structures, and cis-elements were analyzed comprehensively using bioinformatics methods. Expression profiling revealed thatSmHD-Zip Igenes exhibited distinctive tissue-specific patterns and divergent responses to ABA, PEG, and NaCl stresses.SmHD-Zip12responded the most strongly to ABA, PEG, and NaCl, so it was used for transgenic experiments. The overexpression ofSmHD-Zip12significantly increased the content of cryptotanshinone, dihydrotanshinone I, tanshinone I, and tanshinone IIA by 2.89-fold, 1.85-fold, 2.14-fold, and 8.91-fold compared to the wild type, respectively. Moreover, in the tanshinone biosynthetic pathways, the overexpression ofSmHD-Zip12up-regulated the expression levels ofSmAACT,SmDXS,SmIDS,SmGGPPS,SmCPS1,SmCPS2,SmCYP76AH1,SmCYP76AH3, andSmCYP76AK1compared with the wild type.ConclusionsThis study provides information the possible functions of the HD-Zip I family and lays a theoretical foundation for clarifying the functional mechanism of theSmHD-Zip12gene in regulating the synthesis of tanshinone inS. miltiorrhiza.