# Functions of Representative Terpenoids and Their Biosynthesis Mechanisms in Medicinal Plants
## 8 Conclusions and Perspectives  
Over the past decade, advancements in next-generation sequencing techniques, molecular biology techniques, and multi-omics techniques have greatly enhanced our comprehension of the synthesis and regulation of terpenoids in medicinal plants. Environmental factors, structural genes, transcription factors, and transporters have been identified as the pivotal factors influencing the accumulation of terpenoids in these plants. Currently, the development and utilization of key genes or technologies to enhance terpenoid biosynthesis in medicinal plants has become a hot research topic.  
However, our knowledge of terpenoids remains incomplete due to the complex and specific nature of their biosynthesis. To further advance our knowledge of terpenoids, future research should focus on several areas: (1) Although several genes upstream of terpenoid biosynthetic pathways have been isolated and cloned, their precise function in the regulation of terpenoid biosynthesis still needs further experimental validation. In addition, little information is available on the downstream terpenoid biosynthetic pathways in medicinal plants, especially regarding _CYP450_ family genes. Some specific terpene synthesis pathways still need to be improved. (2) Callus, hairy root, and/or transient overexpression/silencing have been used to assess the functions of terpenoid genes in medicinal plants. However, stable genetic transformation systems are not available for various medicinal plants, such as _S. miltiorrhiae_, _G. biloba_, and _T. media_. Therefore, stable genetic transformation and gene editing systems such as the CRISPR-Cas9 system need to be established to achieve biotechnology breeding. (3) Transporters play an essential role in the transport of terpenoids since the biosynthesis and application sites of terpenoids are different in some medicinal plants. Therefore, it is crucial that we identify and characterize transporters of terpenoids in medicinal plants, which are essential for enhancing the accumulation of terpenoids. (4) Genomics, transcriptomics, and metabolomics analyses have provided insights into terpenoid synthesis in medicinal plants. In the future, more attention should be given to the mechanisms of transcriptional regulation in terpenoid synthesis, as well as the construction of networks of transcriptional and post-transcriptional regulation. Additionally, the influence of epigenetics on terpenoid synthesis should also be considered. (5) The development of biosynthetic techniques, such as the use of yeast and other microorganisms, can facilitate the accumulation of specific terpenoids compared to those produced by plants themselves. However, when multiple terpenoids work together to exert medicinal effects, it becomes challenging to achieve similar outcomes through synthesis. In this regard, plants, capable of producing multiple terpenoids, offer additional advantages. Therefore, future research should focus on enhancing biosynthetic techniques to synthesize multiple terpenoids. These studies will be of great significance for the breeding of medicinal plants with high terpenoid content through biotechnology, as well as the production of terpenoid compounds through bioengineering.  
Conceptualization, Q.W. and L.W.; writing--original draft preparation, Q.W., X.Z. and Y.J.; writing--review and editing, Q.W. and L.W.; Visualization, B.J. All authors have read and agreed to the published version of the manuscript.  
This research was funded by the National Natural Science Foundation of China, grant number 31971686, 32171838 and 32101558 and the Natural Science Foundation of Jiangsu Province, grant number, BK20210801.  
The authors declare no conflict of interest.