## 1 Introduction
\begin{table}
\begin{tabular}{c c c c} \hline \hline \multicolumn{2}{c}{**Liposoluble Components**} & \multicolumn{2}{c}{**Water-Soluble Components**} \\ \multicolumn{2}{c}{**(Tanshinones)**} & \multicolumn{2}{c}{**(Phenolic Acids)**} \\ \hline \multirow{2}{*}{**Name**} & **Molecular** & \multirow{2}{*}{**Name**} & **Molecular** \\  & **Structure** & & **Structure** \\ \hline \multirow{2}{*}{Tanshinone I} & \multirow{2}{*}{Rosmarinic acid} & \multirow{2}{*}{
\begin{tabular}{c} **Molecular** \\ **Structure** \\ \end{tabular} } \\  & & & \\ \end{tabular}
\end{table} 
Table 1: The main medicinal active ingredients in _S. milliorrhiza_. CCD1 can cleave carotenoids in flowers and fruits to form aromatic compounds [22; 23]. For example, LeCCD1 symmetrically cleaves multiple carotenoid substrates at the 9,10 (9',10') positions to produce a C14 dialdehyde and two C13 cyclohexones that vary depending on the substrate in _Lycopersicon esculent_[24]. _CCD4_ regulates the homeostasis of carotenoids, and its expression can lead to the breakdown of carotenoids, thereby regulating the color of plants' flowers, fruits, etc. [25; 26]. Some members of the CCD family can also regulate plant growth and development, such as inhibiting AcCCD8 expression in kiwifruit, which can affect plant branch development and delay leaf senescence [27]. The ntccd8 mutants in tobacco (_Nicotiana tabacum_ L.) had increased shoot branching, reduced plant height, an increased number of leaves and nodes, and reduced total plant biomass compared with wild-type plants [28]. _CCD7_ and _CCD8_ have also been shown to be essential genes for the biosynthesis of SLs [29]. Research has shown that members of the CCO family are widely involved in various stress responses of plants. For example, in _Brassica oleracea_, _CCD1_ (Bol044673) and _CCD4_ (Bol009345 and Bol029878) are highly responsive to drought and salt stress [30]. The expression of the saffron _CCD4_ gene can also be highly induced under drought conditions [31]. From this, it can be seen that CCDs not only affect plant odor and color and participate in the synthesis of hormones such as ABA and SLs but also regulate plant responses to various stress conditions. Abscisic acid (ABA) plays a very essential role in enhancing plant stress resistance. When plants are subjected to biological stress such as low temperature and drought, the content of ABA in the plant notably increases, causing changes in physiological and biochemical responses, thereby enhancing the plant's stress resistance [32]. Research has shown that _A. thaliana_ can highly induce the expression of related CCO under drought stress, and its overexpression leads to the accumulation of ABA [33]. In addition, the upregulation of _LeNCED1_ expression in _Lycopersicum esculent_ leaves also increases the seed dormancy rate [34]. These studies suggest that CCO genes can affect the ABA-mediated plant stress response by regulating ABA synthesis. The carotenoid cleavage dioxygenase _SmCCD4_ is highly responsive to drought stress on the basis of our preceding work based on the transcriptome database of _S. miltiorrhiza_. Furthermore, all members of the CCO family in _S. miltiorrhiza_ were screened and structurally analyzed. Finally, a total of 26 SmCCO genes were characterized according to the whole-genome database of _S. miltiorrhiza_. The expression pattern of _SmCCD4_ indicated that this gene is strongly overexpressed in the aboveground tissues of _S. miltiorrhiza_ and showed obvious responses to ABA treatment and drought stress. The overexpression of _SmCCD4_ not only promotes the synthesis of ABA and increases plant antioxidant activity but also regulates the synthesis of the secondary metabolites tanshinone and phenolic acids in _S. miltiorrhiza_.