## 3 Outlook
In addition to microbial systems, plant systems are also functional gene heterologous expression systems that have been applied more often in recent years [105; 106]. Plants themselves contain or encode enzyme genes, organelles with similar structure and function, coenzymes, coenzyme factors and precursors, which facilitate the expression and post-translational modification of botanical proteins. For example, Lycopersicon esculent has been widely used for the production of natural products such as _astaxanthin_[107], _cyanidin_[108], and _flavonols_[109]. _Nicotiana benthamiana_ has been used as a chassis to reconstruct the pathways of several natural products, such as _vinblastine_[110] and _podophyllotoxin_[111]. In the future, we can continue to explore more transient expression systems and try to realize the expression of botanical biopesticides in plant systems. At the same time, the modification of common chassis cells such as _Saccharomyces cerevisiae_ and _E. coli_ was performed. The expression and functional studies of P450 in _E. coli_ were achieved by modifying the membrane localization sequence of the P450 gene [112]. A cytochrome P450 reductase from _Arabidopsis thaliana_ was integrated on the _Saccharomyces cerevisiae_ chromosome to construct a strain WAT11 dedicated to plant P450 expression and functional studies [113]. This strain has been widely used for P450 gene expression and functional studies. In the future, more suitable chassis need to be discovered, and the metabolic capacity of the chassis strain needs to be further optimized. Secondly, optimize the synthesis pathway. The biosensor plays an important role. With the specific sensitivity to the target metabolites, the information of metabolite changes can be outputted in real-time by various signals, which can realize dynamic monitoring and feedback to balance the biosynthetic pathway and improve the yield of natural products [114]. [PERSON] et al. [115] constructed a sensor-actuator circuit for the dynamic control of genome-wide mutation rate, which successfully led to a five-fold and three-fold increase in the yield of _tyrosine_ and _lycopene_. It is believed that the future development of biosensors will further optimize the synthesis pathway and effectively contribute to the research on yield enhancement of natural product genetically engineered bacteria and explore more ways to mine components. Thirdly, the application of computational biology methods can obtain candidate genes and perform functional studies more precisely, effectively reducing workload and improving screening efficiency. The researchers used computational biology to mine the database for possible functional components of natural product biosynthetic pathways and realized the biosynthesis of thebaine and hydrocodone [36], isoquinoline alkaloids [116], and other natural products through functional studies and pathway reconstruction. It is believed that, with plenty of plants and microbial resources as the foundation, and synthetic biology development as the means, the quick advances in the study of botanical biopesticides will be promising. The development of varieties and efficient manufacturing will go hand in hand, driving the development of the entire biopesticide industry and providing powerful support for the healthy and rapid development of green agriculture. **Author Contributions:** [PERSON], [PERSON] and [PERSON] conceived and designed the review; [PERSON] and [PERSON] performed most of the investigation; [PERSON] and [PERSON] provided assistance; [PERSON], [PERSON] and [PERSON] wrote the paper. All authors have read and agreed to the published version of the manuscript. **Funding:** This research was supported by Key-Area Research and Development Program of Guangdong Province (2020B0303070002). **Institutional Review Board Statement:** Not applicable. **Informed Consent Statement:** Not applicable. **Data Availability Statement:** Not applicable. **Conflicts of Interest:** The authors declare no conflict of interest.