The medicinal active ingredients and their associated key enzyme genes are differentially regulated at different growth stages in Cornus officinalis and Cornus controversa

Abstract

Revealing the dynamic accumulation and synthesizing mechanism of medicinal active ingredients will be of great significance for the evaluation and utilization of crops in medicinal industry. Dogwood (Cornus officinalis Sizb. et Zucc.), a perennial deciduous tree in the Cornaceae family, possesses important medicinal values in protecting nerves, treating diabetes and kidney diseases, and preventing inflammation and apoptosis. Dengtaishu (Cornus controversa Hemsl.) is another perennial tree in the Cornaceae family. As a Cornus plant that is phylogenetically close to C. officinalis, it is widely used as horticultural landscape plants. Revealing the difference of active ingredients between the two plants within the same genus as well as its molecular mechanism will help improve resource utilization of medicinal crops. In this study, a systematic analysis on the fruit characters, content of active ingredients and expression of key enzyme genes of C. officinalis and C. controversa was conducted. First, the main fruit characters and active ingredients in fruits and leaves of C. officinalis and C. controversa during different growth stages were determined and analyzed. The key enzyme genes geraniol 10-dehydrogenase (G10H) and secologanin synthase (SLS) in the loganin synthesis pathway of C. officinalis and C. controversa were cloned, and the expression level of G10H and SLS was determined by quantitative real-time PCR (qRT-PCR) in leaves and fruits of the two species at different growth stages. Finally, correlation analysis between the content of loganin and the expression of G10H and SLS was conducted to reveal the possible molecular mechanism of loganin synthesis. The results showed that: (1) The fruit length, seed length, and 100-fruit weight of C. officinalis were significantly higher than those of C. controversa (P < 0.01). (2) The content of total sugar and cornel iridoid glycosides (CIGs) in fruits were significantly higher than those in leaves in both the two species, and they increased significantly with the duration of growth period. (3) The content of six active ingredients in leaves was significantly lower than that in fruits of the two species. Except for 5-hydroxymethylfurfural, the content of other five active ingredients in fruits of C. officinalis was significantly higher than that of C. controversa. (4) The content of loganin, cornuside, and protocatechuate in leaves of C. controversa were significantly higher than that of fruits of C. officinalis. (5) G10H was mainly expressed in the fruits of two species, and the expression in fruits of C. officinalis was significantly higher than that of C. controversa. The expression of SLS in fruits and leaves of C. controversa was significantly higher than that of C. officinalis at late growth stage. (6) Correlation analysis between loganin content and gene expression indicated that there was a positive correlation between the expression of G10H and the content of loganin, while the expression of SLS was negatively correlated with the content of loganin. These results first raise the possibility that C. controversa can be used as an alternative to C. officinalis in resource utilization. Meanwhile, the best harvest time with best quality and high yield for C. officinalis and C. controversa was determined. Furthermore, it was speculated that the significant differences of the expression of G10H and SLS in loganin synthesis pathway might be the main reason for the differences of active ingredients between the two species within the same genus. Taken together, these results will further provide insights into the improvement of both the quality and the yield of medicinal crops using approaches of germplasm breeding and genetic engineering.