The team of Professor Tang Kexuan of Shanghai Jiaotong University and the team of Academician Huang Luqi of the Chinese Academy of Chinese Medical Sciences published an important review in the field of transcriptional regulation of medicinal plants

The active ingredients in medicinal plants have attracted wide attention because of their important role in the treatment of diseases, such as artemisinin for malaria, tanshinone and salvianolic acid for cardiovascular disease, paclitaxel and vinblastine for cancer, and ginsenosides involved in immune regulation
.
The biological and abiotic stress in environmental factors is considered to be one of the core reasons for promoting the accumulation of active ingredients of medicinal plants, and it is also a key factor
in the formation of authentic medicinal materials.
Therefore, what is the molecular mechanism by which environmental factors affect the accumulation of active ingredients in medicinal plants?

Recently, Professor Tang Kexuan's research group of Shanghai Jiao Tong University and the team of Academician Huang Luqi of the Chinese Academy of Chinese Medical Sciences published a title entitled "Transcriptional regulatory network of high-value active ingredients in medicinal" in Trends in Plant Science (IF=22.
012), a top review journal in the field of plant science under Cell plants"
.
In this paper, the transcriptional regulation patterns of biosynthetic pathways of various high-value active ingredients in Artemisia annua, Salvia, Periwinkle, Yew and Panax ginseng were reviewed from the aspects of environmental factors and hormone signals, and the regulatory network of "environmental factors-hormone signaling-transcription factors-active ingredients" and its corresponding research methods were summarized (Figure 1).

It provides a theoretical basis for revealing the adversity effect and the formation mechanism of authentic medicinal materials, and also provides a reference
for the germplasm innovation method of gene editing to "build" the regulatory network of active ingredients in the future.

Fig.
1 Transcriptional regulatory network and multi-omics research methods of active ingredients of medicinal plants

Regulatory networks: environmental factors - hormone signals - transcription factors - active ingredients

Plant hormones, such as jasmonic acid (JA), abscisic acid (ABA), salicylic acid (SA), gibberellin (GA), ethylene (Eth), and indoleacetic acid (IAA), can function in response to abiotic and biological stresses such as drought, heat and cold, hypoxia, ultraviolet radiation, heavy metals, pathogens, and animal feeding, acting as "brokers" between environmental and transcription factors, synergizing or antagonizing the biosynthesis of medicinal plant active ingredients (Figure 1B).
This is one of the reasons why adversity promotes the accumulation of
active ingredients of medicinal plants.
The transcriptional regulation mechanism of biosynthesis of active ingredients of medicinal plants is complex and multi-layered, which is currently a research hotspot
in molecular pharmacognosy.
It is mentioned that ERF, bZIP, bHLH, MYC, MYB, WRKY and other multi-family transcription factors are induced by the environment/hormone, and show significant regulatory ability of active ingredient biosynthesis in different medicinal plants, and finally form a regulatory network
from environmental factors to active ingredients.

The biosynthesis of artemisinin in Artemisia annua is regulated by a variety of environmental factors and hormones, and forms a multi-level transcriptional regulatory network (Figure 2).

AaWRKY1, AaORA, AaMYC2, AabHLH1, AaGSW1 and AaTCP14-AaORA complex mediate JA signaling positively regulating artemisinin synthesis.
AabZIP1 and AaABF3 mediate ABA to promote artemisinin synthesis; The photosignal transcription factor AaHY5 mediates light signal to promote artemisinin synthesis by activating AaGSW1 expression.
AaWRKY9 positively regulates artemisinin synthesis through JA and optical signal interaction, and AaTCP15 is induced by JA and ABA to promote artemisinin accumulation.
In addition, AaTGA6 of SA pathway, cold-induced AabHLH112 and ethylene-induced negative regulator AaEIN3 were involved in the regulation of artemisinin synthesis
.

Fig.
2 Transcriptional regulatory network of artemisinin biosynthesis in Artemisia annua

Construction method: hormone signal transduction and transcriptional regulation

More than a decade ago, homologous cloning was the primary method
used to isolate transcription factors from Artemisia annua and salvia.
Nowadays, based on genomics, transcriptomics, proteomics, interactomics and metabolomics, the screening process
of key proteins and transcription factors of the signaling pathway of medicinal plant hormones has been greatly promoted.

In terms of hormone signal transduction, in vitro and in vitro binding experiments such as yeast double hybridization and sieve library (Y2H), protein pull-down, bimolecular fluorescence complementation (BiFC), firefly luciferase fragment complementary imaging technology (LCI), and co-immunoprecipitation (CoIP) can be used to screen and verify the interaction proteins and interaction methods in the signal transduction pathway.
In terms of transcriptional regulatory network, yeast single hybridization and sieve library (Y1H), gel blocking experiment (EMSA), DNA affinity purification sequencing (DAP-seq), double luciferase detection (Dual-LUC), chromatin co-immunoprecipitation (ChIP) and other in vitro and in vitro binding experiments, combined with phenotypic analysis of transgenic plants, can be used to screen and verify transcription factors and target genes
in the process of transcription regulation.
In an iterative approach, researchers are able to efficiently discover active ingredients, decipher relevant biosynthetic pathways, and reveal regulatory network mechanisms (Figure 1A).

prospect

With the deepening of research in the field of medicinal plant regulation, the regulatory network that controls the biosynthesis of active ingredients is gradually revealed, and the formation mechanism of authentic medicinal materials will gradually become clear
.
In the foreseeable future, precise gene editing technology can provide a theoretical basis
for germplasm innovation of medicinal plants by "building" specific regulatory networks to simulate the adverse effect to reshape the physiological process of medicinal plants or strengthen the accumulation of target active ingredients.

Scientific problems that need to be solved in this field

1.
To date, the molecular mechanism of transcriptional regulation of biosynthesis of active ingredients remains unclear
in most medicinal plants.
How can we combine multiomics techniques such as single-cell omics, proteomics, epigenemics, phenomics, and especially genomics, transcriptomics, and metabolomics to more effectively dissect molecular mechanisms?

2.
How do we identify the core transcription factors involved in the biosynthesis of active ingredients, similar to AtMYB12 in Arabidopsis, that can activate multiple genes in a single biosynthetic pathway?

3.
What are the reported relationships between transcription factors that regulate the biosynthesis of active ingredients? How do transcription factors form transcriptional regulatory networks in medicinal plants?

4.
In medicinal plants, is the regulatory network of JA-TFs the core network for regulating the biosynthesis of active ingredients?

5.
How do different signals, such as JA and light, JA and ABA, JA and GA, interact to regulate the biosynthesis of active ingredients of medicinal plants?

6.
Can transcriptional regulatory networks control the accumulation of active ingredients without affecting the normal growth and development of medicinal plants?

Assistant researcher Zheng Han, assistant researcher Fu Xueqing, Dr.
Shao Jin and lecturer Tang Yueli of Southwest University are co-first authors of the paper, and Professor Tang Kexuan of Shanghai Jiao Tong University and Academician Huang Luqi of the Chinese Academy of Chinese Medical Sciences are the co-corresponding authors
of the paper.
This work has been supported
by the central government-level major increase and decrease project "Capacity Building for the Sustainable Utilization of Precious Chinese Medicine Resources" (2060302), the National Key Research and Development Program (2018YFA0900600), and the translational medicine research (20190104) of Shanghai Jiao Tong University.

Link to paper: https://doi.
org/10.
1016/j.
tplants.
2022.
12.
007