LIFE SCIENCE

Survival in adversity, medicinal herbs get authentic


Xinhui tangerine peel, produced in Xinhui District, Jiangmen City, Guangdong Province, is a local medicinal material designated by the Chinese Pharmacopoeia as a local medicinal material of Guangxi Tangerine Peel, and its quality is significantly higher than that grown around Guangdong and other regions.

Tea branch citrus fruit Photo courtesy of interviewee

Photo courtesy of interviewee

How exactly is the authenticity of medicinal herbs produced? Why can good authentic Chinese medicinal herbs grow in adversity?

On March 28, South China Agricultural University and BGI Institute of Life Sciences published a research paper in the international academic journal Microbiome. This study reveals the special soil environment and the biological mechanism of how microbial composition promotes the synthesis and accumulation of monoterpenes, the active ingredient of Guangchen Pi in the real estate area. This achievement has made a theoretical breakthrough in the analysis of the formation mechanism of the authenticity of Guangchen peel, which provides a new idea for the evaluation of the authenticity of Chinese medicinal materials, and also provides technical support for the research and development of special bacterial fertilizers for authentic medicinal materials.

Is authenticity related to special environments?

Tangerine peel medicinal materials are divided into “tangerine peel” and “broad tangerine peel”. Guangchen Pi refers to the peel of Citrus reticulate ‘Chachi’ fruit planted in Xinhui area of Guangdong, which is one of the first eight Lingnan traditional Chinese medicines protected by legislation in Guangdong Province.

Wu Hong, co-corresponding author of the paper and professor of the Medicinal Plant Research Center of South China Agricultural University, introduced that flavonoids and terpenes are two important functional components in Guangchen peel, and play an important role in the quality evaluation and clinical efficacy of Guangchen peel.

“The synthesis of functional components of medicinal plants is a systematic process from the genetic regulation of species to the multi-dimensional interaction between climate, soil nutrients, and root microorganisms of the production area, but the biological mechanism of its authentic formation is still insufficient.” Liu Huan, co-corresponding author of the paper and a researcher at the BGI Institute of Life Sciences, said that under the same genetic background, the biological mechanism of how soil nutrition and root microbiome affect the synthesis and accumulation of plant medicinal components is poorly understood.

Metabolome detection found that there were 18 different types of volatile oil components in the peel of tea citrus. Among them, the contents of 7 monoterpenes (including β-myrcene, α-pinene, β-pinene, α-terpinene, etc.) were significantly higher in the real estate area than in the non-real estate area. These monoterpene components in the peel have antioxidant, antibacterial, antiviral, anti-inflammatory and anti-tumor effects, and are important active ingredients in Guangchen peel, which can be used as indicators for the quality evaluation of raw materials of Guangchen peel.

It has been known that Chinese medicine must be planted in adversity, and good Chinese medicinal materials can grow in adversity. So what kind of special environment does the Xinhui production area have? How do these special environmental factors regulate the synthesis of medicinal ingredients of tangerine peel?

By detecting the soil physicochemical properties of Daojiang and non-Daojiang areas, the researchers found that the soil in Daojiang area has high nutrient content, which provides sufficient nutrients for plants. In addition, the salinity in the soil of the Dao real estate area can reach up to 0.49 (mean 0.32), the salinity in other production areas is up to 0.16 (mean value of 0.11), the salt in the soil of the Dao real estate area is 3.2 times higher than that of other production areas, and the higher salinity affects the physiological metabolism of plants, which is salt stress.

Originally, Xinhui was located at the intersection of the sea and the river (the tributary of the Xijiang River, the Tan River, and the mouth of Yinzhou Lake). Every year during the flood season, the Xijiang River will bring the soil elements of the Yunnan-Guizhou Plateau to Yinzhou Lake, meet with the water of the Tan River, and form a unique “three water integration” and “salty and light intersection” water and soil characteristics when the South China Sea tide is irrigated, and its rich nutrients and seawater salts have achieved a special environment with high nutrition and high salinity of Xinhui soil, and at the same time introduced a large number of microbial taxa that are resistant to salt stress.

Tea citrus sample collection Photo courtesy of interviewee

They collected soil and root microorganisms, root, leaf and fruit samples from seven orchards including Dao Real Estate Area (Guangdong Xinhui) and Non-Dao Real Estate Area (Guangdong Huizhou, Taishan and Guangxi Guigang), and systematically explored the intrinsic correlation mechanism of “soil nutrients-root microorganisms-quality components of Guangchen peel” by multi-omics method, and studied the mechanism of the formation of Guangchen peel quality from three dimensions: plant gene expression, soil nutrients and root microbiome.

The soil environment affects the accumulation of active ingredients of medicinal herbs

“Different soil environments affect differential expression of root genes.” Liu Huan introduced that the correlation between special soil nutrients and root high expression genes in Daoreal Land Area found that the special soil environment (such as high salt, Mg, Mn and K) in Daoreal Land Area was significantly correlated with the expression of plant salt stress response genes and terpene backbone synthetase genes.

By detecting the gene transcription differences in roots, leaves and fruits, it was found that the genes related to terpene synthesis, salt stress related genes and immune response were highly expressed in the Daoji area, and these highly expressed genes were significantly positively correlated with the content of seven single-post components.

“It suggests that the expression of these genes may affect the accumulation of monoterpene components in the Daojia area.” In addition, the number of genes associated with biotic and abiotic stress responses in the root samples of the Dao real estate area is higher than that in the non-Dao real estate area, indicating that the biological (such as microbial composition) and abiotic environment (soil nutrients) conditions in the soil of the Dao real estate area and the non-Dao real estate area may be different.

Wu Hong said that the high nutrients in the soil of the Daoreal estate area provided sufficient nutrients for the growth and development of plants, Mg and Mn as coenzymes of monoterpene synthase improved the activity of monoterpene synthetase, and the high salinity stress in the soil promoted the synthesis of monoterpene components through salt stress reaction.

In addition, the microbial composition of the root system can regulate the absorption of plant nutrients, help plants resist stress and adversity, and affect the synthesis of functional components of medicinal plants. The researchers further found that there were significant differences in the composition of rhizosphere soil and root microorganisms in the Dao and non-Dao real estate areas.

Liu Huan introduced that there are a large number of salt-tolerant genes and terpene synthesis-related genes in the genome of a large number of microorganisms in the rhizosphere soil enriched in the Daoreal estate area, indicating that these microorganisms have the characteristics of salt tolerance and have the potential to synthesize terpenes. By correlating microbial composition with monoterpene composition, rhizosphere and intraroot microbial taxa with significant correlation with monoterpene content were identified.

Provide a basis for improving the quality of Chinese medicinal materials

So what is the mechanism by which rhizosphere soil and its microbial community affect the accumulation of monoterpene components? They then launched further research.

By isolating rhizosphere and intra-root microbial strains, synthetic biota experiments confirmed that Streptomyces Strep-4 from rhizosphere soil can promote the synthesis and accumulation of monoterpenoids, the active ingredient of tea branch, by inducing systemic resistance in plants.

At the same time, the addition of Serra-11, a symbiotic Serrascilla strain in the root, can further enhance the effect of Strep-4 of Strep.

Genome sequencing found that Serrascratia serra-11 has the potential to synthesize monoterpenes, which can directly enter the root to synthesize monoterpene precursors, thereby further enhancing the accumulation of monoterpenes.

“These studies show that rhizosphere soil and endosymbiotic bacteria jointly promote the accumulation of monoterpenoids in citrus fruit by triggering plant immune responses or providing plants with monoterpene synthesis intermediates.” Wu Hong said.

Liu Huan told China Science News that through metagenomics to study the structure and function of the root microbiome and analyze the association with the phenotype of plants, we can scientifically discover microbial groups related to plant growth, yield, quality and disease resistance, and discover a large number of species taxa and genetic resources of microorganisms with potential application value.

The researchers systematically studied the correlation mechanism of the efficient synthesis of functional components (terpenes) from the three dimensions of soil nutrients-root microorganisms-plant gene regulation patterns. This study identified the key soil nutrients and target microbial groups that affect the quality components of Chinese medicinal materials and their mechanism of action, scientifically revealed the causes of the “authenticity” of authentic medicinal materials, provided a scientific basis for the formula fertilization of Chinese medicinal materials, the separation of beneficial microorganisms, planting planning and quality improvement, and provided an important guarantee for the high-quality and sustainable development of the Chinese medicinal materials industry.

However, Wu Hong emphasized that the stress of high salinity promotes the expression of genes related to salt stress in tea branch citrus, but the rationality of salt stress and how salt stress response genes affect the synthesis of functional components need to be further verified by experiments. (Source: China Science News, Li Chen, Zhu Hanbin)

Related paper information:https://doi.org/10.1186/s40168-023-01504-2



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