Carotenoid Cleavage Dioxygenase Gene CCD4 Enhances Tanshinone Accumulation and Drought Resistance in Salvia miltiorrhiza.

Danshen (Salvia miltiorrhiza Bunge) is a perennial herbaceous plant of the Salvia genus in the family Lamiaceae. Its dry root is one of the important traditional Chinese herbal medicines with a long officinal history. The yield and quality of S. miltiorrhiza are influenced by various factors, among which drought is one of the most significant types of abiotic stress. Based on the transcriptome database of S. miltiorrhiza, our research group discovered a carotenoid cleavage dioxygenase gene, SmCCD4, belonging to the carotenoid cleavage oxygenase (CCO) gene family which is highly responsive to drought stress on the basis of our preceding work. Here, we identified 26 CCO genes according to the whole-genome database of S. miltiorrhiza. The expression pattern of SmCCD4 showed that this gene is strongly overexpressed in the aboveground tissue of S. miltiorrhiza. And by constructing SmCCD4 overexpression strains, it was shown that the overexpression of SmCCD4 not only promotes the synthesis of abscisic acid and increases plant antioxidant activity but also regulates the synthesis of the secondary metabolites tanshinone and phenolic acids in S. miltiorrhiza. In summary, this study is the first in-depth and systematic identification and investigation of the CCO gene family in S. miltiorrhiza. The results provide useful information for further systematic research on the function of CCO genes and provide a theoretical basis for improving the yield and quality of S. miltiorrhiza.