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The composition and stability of the microbial community structure of roots and root zone soils play a key role in the healthy growth of plants. We examined the distribution characteristics of phenolic acids and saponins, as well as microbial communities in the root space (root endosphere, rhizoplane soil, rhizosphere soil, and bulk soil) of healthy and root rot disease-affected Panax notoginseng. The results showed that after infection with root rot, the rhizoplane soil exhibited significant decreases in organic matter and hydrolyzable nitrogen and significant increases in available phosphorus, available potassium, and total nitrogen. The contents of phenolic acids (except benzoic acid) and ginsenoside Rg2 in the root endosphere significantly increased. Ferulic acid and p-hydroxybenzoic acid in the rhizoplane soil significantly increased. Rhodococcus increased significantly in the root endosphere, rhizoplane, and rhizosphere soil; Nitrospira decreased significantly in the rhizoplane, rhizosphere, and bulk soil; and Plectosphaerella decreased significantly in the root endosphere and rhizoplane soil. Moreover, the accumulation of most autotoxins can promote the growth of pathogens. In summary, the spatial autotoxic substances and microbial community differences in P. notoginseng roots jointly induce the occurrence of root rot. IMPORTANCE Panax notoginseng is highly susceptible to soil-borne diseases induced during planting, and root rot, which usually occurs in the root and stem parts of the plant, is the most severe. We divided the root environment of P. notoginseng into four parts (root endosphere, rhizoplane soil, rhizosphere soil, and bulk soil) and studied it with unplanted soil as the control. In this study, we examined the changes in the content of autotoxic substances in the root space of P. notoginseng, along with the interplay between these substances and microorganisms. This study revealed the mechanism underlying root rot and provided a theoretical basis for alleviating continuous cropping obstacles in P. notoginseng. [ABSTRACT FROM AUTHOR]

Background. Autotoxicity is an intraspecific manifestation of allelopathy in plant species. The specialized metabolites and their derivatives that cause intraspecific allelopathic inhibition in the plant are known as autotoxic substances. Consequently, autotoxic substances production seriously affects the renewal and stability of ecological communities. Methods. This article systematically summarizes the types of autotoxic substances present in different plants. They mainly include phenolic compounds, terpenoids, and nitrogenous organic compounds. Phenolic coumarins are the main autotoxic substances in many plants. Therefore, we also discuss differences in coumarin types and content among plant varieties, developmental stages, and tissue parts, as well as their mechanisms of autotoxicity. In addition, we review the metabolic pathways involved in coumarin biosynthesis, the key enzymes, genes, and transcription factors, as well as factors affecting coumarin biosynthesis. Results. Coumarin biosynthesis involves three stages: (1) the formation of the coumarin nucleus; (2) acylation, hydroxylation, and cyclization; (3) structural modification. The key enzymes involved in the coumarin nuclear formation stage include PAL, C4H, 4CL, HCT, CAOMT, COSY, F6'H, and CCoAOMT1, and the key genes involved include BGA, CYP450 and MDR, among others. Ortho-hydroxylation is a key step in coumarin biosynthesis and PS, COSY and S8H are the key enzymes involved in this process. Finally, UGTs are responsible for the glycosylation modification of coumarins, and the MaUGT gene may therefore be involved in coumarin biosynthesis. Conclusion. It is important to elucidate the autotoxicity and anabolic mechanisms of coumarins to create new germplasms that produce fewer autotoxic substances. [ABSTRACT FROM AUTHOR]

Abstract Background In faba bean, continuous cropping severely affects plant growth and increases the incidence of fusarium wilt due to the accumulation of pathogens and autotoxic substances. The intercropping of faba bean and wheat is commonly used to alleviate the occurrence of fusarium wilt in the faba bean. Objective To investigate the role of Fusarium oxysporum f. sp. Fabae(FOF) and benzoic acid in the occurrence of faba bean fusarium wilt and unravel the potential mechanism of intercropping in alleviating its occurrence. Methods Hydroponic experiment was carried out using monocropping faba bean (M) and intercropping faba bean and wheat (I) patterns under FOF alone stress (M + F, I + F), FOF and benzoic acid double stress (M + F + B, I + F + B). The growth of faba bean seedlings under FOF and benzoic acid dual stresses were analyzed as well as the protein expression profile of monocropping and intercropping faba bean roots. Result Under FOF stress, the growth of faba bean seedlings was inhibited, and the inhibitory effect was enhanced under the dual stress of FOF and benzoic acid. However, faba bean-wheat intercropping alleviated the inhibitory effect of FOF and benzoic acid on faba bean growth. In faba bean, the up-regulated protein was involved in different functions, such as redox, hydrogen peroxide decomposition, and metabolic processes under FOF stress (M + F, I + F) compared to the control. Compared with FOF stress (M + F, I + F), under the dual stress of FOF and benzoic acid (M + F + B, I + F + B), the up-regulated protein in faba bean were involved in intracellular redox balance, defense, and maintenance of cell integrity. Compared with monocropping (M, M + F, M + F + B), the up-regulated protein function of intercropping(I, I + F, I + F + B) was mainly involved in the biosynthesis of secondary metabolites, redox balance, biological carbon fixation of photosynthesis, and so on. KEGG enrichment analysis results showed that intercropping increased ethylene and jasmonic acid synthesis and other related pathways to improve resistance against fusarium wilt in the faba bean. Conclusion The growth of faba bean was inhibited under FOF stress and the inhibitory effect was enhanced under the dual stress of FOF and benzoic acid, which promoted the occurrence of faba bean fusarium wilt. This might be due to the down-regulation of energy and cytoplasmic matrix proteins under FOF and benzoic acid stress. The faba bean wheat intercropping alleviated the inhibition of FOF and benzoic acid stress by up-regulating the biosynthesis of secondary metabolites, redox homeostasis, photosynthetic carbon fixation, and other related proteins. Besides, it also promoted the biosynthesis of ethylene, and jasmonic acid, improved the resistance of faba bean plants, and alleviated the occurrence of faba bean fusarium wilt. This provides a theoretical basis for the determination of jasmonic acid and ethylene content.

Background: In faba bean, continuous cropping severely affects plant growth and increases the incidence of fusarium wilt due to the accumulation of pathogens and autotoxic substances. The intercropping of faba bean and wheat is commonly used to alleviate the occurrence of fusarium wilt in the faba bean. Objective: To investigate the role of Fusarium oxysporum f. sp. Fabae(FOF) and benzoic acid in the occurrence of faba bean fusarium wilt and unravel the potential mechanism of intercropping in alleviating its occurrence. Methods: Hydroponic experiment was carried out using monocropping faba bean (M) and intercropping faba bean and wheat (I) patterns under FOF alone stress (M + F, I + F), FOF and benzoic acid double stress (M + F + B, I + F + B). The growth of faba bean seedlings under FOF and benzoic acid dual stresses were analyzed as well as the protein expression profile of monocropping and intercropping faba bean roots. Result: Under FOF stress, the growth of faba bean seedlings was inhibited, and the inhibitory effect was enhanced under the dual stress of FOF and benzoic acid. However, faba bean-wheat intercropping alleviated the inhibitory effect of FOF and benzoic acid on faba bean growth. In faba bean, the up-regulated protein was involved in different functions, such as redox, hydrogen peroxide decomposition, and metabolic processes under FOF stress (M + F, I + F) compared to the control. Compared with FOF stress (M + F, I + F), under the dual stress of FOF and benzoic acid (M + F + B, I + F + B), the up-regulated protein in faba bean were involved in intracellular redox balance, defense, and maintenance of cell integrity. Compared with monocropping (M, M + F, M + F + B), the up-regulated protein function of intercropping(I, I + F, I + F + B) was mainly involved in the biosynthesis of secondary metabolites, redox balance, biological carbon fixation of photosynthesis, and so on. KEGG enrichment analysis results showed that intercropping increased ethylene and jasmonic acid synthesis and other related pathways to improve resistance against fusarium wilt in the faba bean. Conclusion: The growth of faba bean was inhibited under FOF stress and the inhibitory effect was enhanced under the dual stress of FOF and benzoic acid, which promoted the occurrence of faba bean fusarium wilt. This might be due to the down-regulation of energy and cytoplasmic matrix proteins under FOF and benzoic acid stress. The faba bean wheat intercropping alleviated the inhibition of FOF and benzoic acid stress by up-regulating the biosynthesis of secondary metabolites, redox homeostasis, photosynthetic carbon fixation, and other related proteins. Besides, it also promoted the biosynthesis of ethylene, and jasmonic acid, improved the resistance of faba bean plants, and alleviated the occurrence of faba bean fusarium wilt. This provides a theoretical basis for the determination of jasmonic acid and ethylene content. [ABSTRACT FROM AUTHOR]

The composition and stability of the microbial community structure of roots and root zone soils play a key role in the healthy growth of plants. We examined the distribution characteristics of phenolic acids and saponins, as well as microbial communities in the root space (root endosphere, rhizoplane soil, rhizosphere soil, and bulk soil) of healthy and root rot disease-affected Panax notoginseng . The results showed that after infection with root rot, the rhizoplane soil exhibited significant decreases in organic matter and hydrolyzable nitrogen and significant increases in available phosphorus, available potassium, and total nitrogen. The contents of phenolic acids (except benzoic acid) and ginsenoside Rg2 in the root endosphere significantly increased. Ferulic acid and p-hydroxybenzoic acid in the rhizoplane soil significantly increased. Rhodococcus increased significantly in the root endosphere, rhizoplane, and rhizosphere soil; Nitrospira decreased significantly in the rhizoplane, rhizosphere, and bulk soil; and Plectosphaerella decreased significantly in the root endosphere and rhizoplane soil. Moreover, the accumulation of most autotoxins can promote the growth of pathogens. In summary, the spatial autotoxic substances and microbial community differences in P. notoginseng roots jointly induce the occurrence of root rot.IMPORTANCE Panax notoginseng is highly susceptible to soil-borne diseases induced during planting, and root rot, which usually occurs in the root and stem parts of the plant, is the most severe. We divided the root environment of P. notoginseng into four parts (root endosphere, rhizoplane soil, rhizosphere soil, and bulk soil) and studied it with unplanted soil as the control. In this study, we examined the changes in the content of autotoxic substances in the root space of P. notoginseng , along with the interplay between these substances and microorganisms. This study revealed the mechanism underlying root rot and provided a theoretical basis for alleviating continuous cropping obstacles in P. notoginseng ., Competing Interests: The authors declare no conflict of interest.

Alfalfa long-term continuous cropping (CC) can pose a serious threat to alfalfa production. However, the mechanism of alfalfa CC obstacle is unclear as of today. Our preliminary study showed that the main factors of CC obstacle were not the lack of nutrients or water in alfalfa rhizosphere soils. Further, we evaluated physic-chemical property, microbial population structure, and metabolite differences of alfalfa rhizosphere soils with CC for 1, 7, and 14 years based on analysis of metabolomics and microbiomics. Four phenolic acid metabolites, including p-coumaric acid, ferulic acid, vanillic acid, and p-hydroxybenzoic acid, were found to have significant differences among different CC years, which may be the key factors of CC obstacle. Among them, p-coumaric acid and ferulic acid could significantly decrease the germination rate of alfalfa seeds by 21.11 and 16.67% at the concentration of 100 μg/mL and the height (root length) of alfalfa seedlings by 21% (32.9%) and 13.72% (16.45%). Moreover, these metabolites could effectively promote the growth of some pathogenic fungi, causing alfalfa root rot. Among them, p-coumaric acid obviously and significantly aggravated the occurrence of alfalfa root rot. With the increase of CC years, soil microbial community changed from fungi to bacteria; fungi decreased by 10.83%, fungi increased by 8.08%, and beneficial microorganisms decreased with the increase of CC years. Field analysis and experimental verification showed that the above results were consistent with that of CC obstacle in the field. Among the key metabolites, the autotoxicity of p-coumaric acid was the strongest. This study fully proved that the continuous accumulation of autotoxic substances in alfalfa rhizosphere was the key factor causing alfalfa CC obstacles. [ABSTRACT FROM AUTHOR]

Alfalfa long-term continuous cropping (CC) can pose a serious threat to alfalfa production. However, the mechanism of alfalfa CC obstacle is unclear as of today. Our preliminary study showed that the main factors of CC obstacle were not the lack of nutrients or water in alfalfa rhizosphere soils. Further, we evaluated physic-chemical property, microbial population structure, and metabolite differences of alfalfa rhizosphere soils with CC for 1, 7, and 14 years based on analysis of metabolomics and microbiomics. Four phenolic acid metabolites, including p-coumaric acid, ferulic acid, vanillic acid, and p-hydroxybenzoic acid, were found to have significant differences among different CC years, which may be the key factors of CC obstacle. Among them, p-coumaric acid and ferulic acid could significantly decrease the germination rate of alfalfa seeds by 21.11 and 16.67% at the concentration of 100 μg/mL and the height (root length) of alfalfa seedlings by 21% (32.9%) and 13.72% (16.45%). Moreover, these metabolites could effectively promote the growth of some pathogenic fungi, causing alfalfa root rot. Among them, p-coumaric acid obviously and significantly aggravated the occurrence of alfalfa root rot. With the increase of CC years, soil microbial community changed from fungi to bacteria; fungi decreased by 10.83%, fungi increased by 8.08%, and beneficial microorganisms decreased with the increase of CC years. Field analysis and experimental verification showed that the above results were consistent with that of CC obstacle in the field. Among the key metabolites, the autotoxicity of p-coumaric acid was the strongest. This study fully proved that the continuous accumulation of autotoxic substances in alfalfa rhizosphere was the key factor causing alfalfa CC obstacles.

Background: Autotoxicity is an intraspecific manifestation of allelopathy in plant species. The specialized metabolites and their derivatives that cause intraspecific allelopathic inhibition in the plant are known as autotoxic substances. Consequently, autotoxic substances production seriously affects the renewal and stability of ecological communities., Methods: This article systematically summarizes the types of autotoxic substances present in different plants. They mainly include phenolic compounds, terpenoids, and nitrogenous organic compounds. Phenolic coumarins are the main autotoxic substances in many plants. Therefore, we also discuss differences in coumarin types and content among plant varieties, developmental stages, and tissue parts, as well as their mechanisms of autotoxicity. In addition, we review the metabolic pathways involved in coumarin biosynthesis, the key enzymes, genes, and transcription factors, as well as factors affecting coumarin biosynthesis., Results: Coumarin biosynthesis involves three stages: (1) the formation of the coumarin nucleus; (2) acylation, hydroxylation, and cyclization; (3) structural modification. The key enzymes involved in the coumarin nuclear formation stage include PAL, C4H, 4CL, HCT, CAOMT, COSY, F6'H, and CCoAOMT1, and the key genes involved include BGA, CYP450 and MDR, among others. Ortho-hydroxylation is a key step in coumarin biosynthesis and PS, COSY and S8H are the key enzymes involved in this process. Finally, UGTs are responsible for the glycosylation modification of coumarins, and the MaUGT gene may therefore be involved in coumarin biosynthesis., Conclusion: It is important to elucidate the autotoxicity and anabolic mechanisms of coumarins to create new germplasms that produce fewer autotoxic substances., Competing Interests: The authors declare there are no competing interests., (©2023 Wu et al.)