Polygonum cuspidatum Sieb. et Zucc is an important industrial crop because it contains a large amount of medicinal secondary metabolites (such as polydatin, resveratrol, chrysophanol, and emodin). However, it is unclear whether root endophytic fungi increase the content of secondary metabolites in the plant. This study aimed to analyze the effects of Funneliformis mosseae (Fm) and Piriformospora indica (Pi) alone or in combination on plant growth, root morphology, thirteen sugars concentrations, and six secondary metabolites (physcion, chrysophanol, emodin, aloe-emodin, polydatin, and resveratrol) concentrations of P. cuspidatum. After 11 weeks of the fungal inoculation, the roots could be colonized by Fm and Pi single or in combination, along with the higher root colonization frequency of Fm > Pi > Fm + Pi in the descending order. In addition, Fm and Pi improved plant growth performance (plant height, stem diameter, leaf number, and shoot and root biomass) and root morphology (average diameter, maximum diameter, total length, area, and volume) to varying degrees, depending on fungal inoculations, in which Pi displayed a relatively better effect on plant growth. Single Fm and Pi inoculation significantly increased three disaccharides (sucrose, maltose, and trehalose) accumulation, while dual inoculum (Fm + Pi) only elevated sucrose concentrations. Most monosaccharides concentrations, such as D-arabinose, D-galactose, D-sorbitol, D-fructose, glucose, and L-rhamnose were not altered or inhibited by the endophytic fungi, except the increase in L-fucose and inositol. All fungal treatments significantly increased root chrysophanol and resveratrol concentrations, while decreased aloe-emodin concentrations. In addition, single Pi and dual Fm + Pi increased emodin concentrations, and single Fm and dual Fm + Pi elevated physcion and polydatin concentrations. It was concluded that Fm and Pi promoted the growth of P. cuspidatum, and the combination of Fm and Pi was more conducive to the production of some secondary metabolites than single inoculation.

Medicinal plants are well known to have the advantages of high concentration of medicinal ingredients having clinical importance, curative value, small toxic and side effects. Important compounds viz., paclitaxel, camptothecin, and vincristine have been developed from medicinal plants as first-line of clinical drugs, leading to their consistently increasing demand globally. However, the destruction of natural environment due to excessive mining threatened such resources jeopardizing the successful growing of medicinal plants. A group of beneficial arbuscular mycorrhizal (AM) fungi is known to exist in the rhizosphere of medicinal plants, which can establish a reciprocal symbiosis with their roots, namely arbuscular mycorrhizas. These AM fungi are pivotal in the habitat adaptation of medicinal plants. Studies have demonstrated that AM fungi aided in growth promotion and nutrient absorption of medicinal plants, thereby, accelerating the accumulation of medicinal ingredients and aiding resistance against abiotic stresses such as drought, low temperature, and salinity. An AM-like fungus Piriformospora indica is known to be cultured in vitro without roots, later showed analogous effects of AM fungi on medicinal plants. These fungi provide new mechanistic pathways towards the artificial cultivation of medicinal plants loaded with ingredients in huge demand in international market. This review provides an overview of the diversity of AM fungi inhabiting the rhizosphere of medicinal plants, and analyzes the functioning of AM fungi and P. indica, coupled with future lines of research.

Polygonum cuspidatum Sieb. et Zucc. is a major raw material for the extraction of drugs such as resveratrol, while the over-exploitation of P. cuspidatum decreases the yield and drug components. The purpose of this study was to analyze the effect of inoculation with root endophytic fungi Funneliformis mosseae and Piriformospora indica singly or in combination in biomass production, physiological activities (e.g., chlorophyll, soluble protein, and gas exchange) and main medicinal ingredients of P. cuspidatum, accompanied by the expression levels of associated genes in resveratrol biosynthesis. Single and co-inoculation with P. indica significantly improved shoot and root biomass production, and single and co-inoculation with F. mosseae and P. indica, especially single P. indica, significantly promoted leaf chlorophyll and soluble-protein concentrations and improved leaf gas exchange, including photosynthetic rate, transpiration rate, stomatal conductance, and intercellular CO2 concentration. The application of endophytic fungi increased resveratrol and polydatin concentrations, while it affected chrysophanol, emodin, and physcion concentrations in a complex manner. In addition, F. mosseae inoculation and co-inoculation induced the expression of PcCRS1, PcRS11, PcRS, and PcSTS, and only single F. mosseae and P. indica inoculation up-regulated the expression of PcCHS1 and PcCHS2. It was concluded that endophytic fungi accelerated biomass production, leaf physiological activity, and resveratrol accumulation in P. cuspidatum, which was associated with the up-regulation of related gene expression in resveratrol biosynthesis.

The medicinal plant Polygonum cuspidatum Sieb. Et Zucc is rich in stilbenes (e.g., polygonin and resveratrol) and anthraquinones (e.g., emodin) for the therapy of human diseases, while how to increase the growth and medicinal composition concentrations of P. cuspidatum has become an urgent issue. The aim of the present study was to evaluate the effects of inoculation with an arbuscular mycorrhizal (AM) fungus, Funneliformis mosseae, on plant growth, phosphorus (P) acquisition, medicinal component concentrations, and expressions of resveratrol synthesis-associated enzyme genes of P. cuspidatum at two P levels (0 M and 0.2 M). P supply (0.2 M) stimulated root AM fungal colonization rate. F. mosseae inoculation significantly improved growth performance (height, diameter, and biomass) and root morphology (diameter, length, and projected area), irrespectively of substrate P levels. P supply and F. mosseae distinctly increased soil acid and neutral phosphatase activities, as well as root P concentrations. P supply increased root physcion and resveratrol concentrations in inoculated and uninoculated plants, along with up-regulated expressions of PcCHS1, PcCRS1, PcRS11, and PcSTS. AM plants represented significantly higher root aloe-emodin, chrysophanol, emodin, physcion, polydatin, and resveratrol concentrations than non-AM plants irrespective of P levels, coupled with up-regulated expressions of PcCHS1, PcCHS2, PcRS11, PcRS, and PcSTS. It is concluded that 0.2 M P supply and F. mosseae inoculation promoted chrysophanol, physcion, polydatin, and resveratrol concentrations of P. cuspidatum, with the increase in resveratrol associated with up-regulated expressions of related genes.

Arbuscular mycorrhizal fungi (AMF) participate in the process of plant secondary metabolism and thus affect the production of secondary metabolites. However, it is not clear whether and how AMF affect the growth and secondary metabolites of Polygonum cuspidatum, a medicinal plant rich in resveratrol and polygonin, under different phosphorus (P) levels. This study was performed to analyze the effects of Glomus mosseae on the growth, leaf gas exchange, P concentration, active ingredient concentrations, and expressions of associated genes of P. cuspidatum under P-deficient (0 mol/L P) and P-sufficient (0.2 mol/L P) conditions. The root mycorrhizal colonization rate of inoculated plants was 62.53–73.18%. G. mosseae improved shoot and root biomass as well as leaf P levels to some extent, but the improvement was more prominent under P-sufficient than P-deficient conditions. The fungal colonization also significantly increased leaf photosynthetic rate, stomatal conductance, transpiration rate, and intercellular CO2 concentration, which was more prominent under P-deficient rather than P-sufficient conditions. P addition promoted the concentration of active medicinal components in leaves, especially in uninoculated plants. G. mosseae distinctly raised leaf chrysophanol, emodin, polydatin, and resveratrol concentrations, which was more prominent under P-deficient conditions. However, physcion was raised by G. mosseae only under P-sufficient conditions. AMF and P addition up-regulated expressions of PcCRS1, along with the up-regulation of PcRS11 by P addition and PcRS11 and PcSTS by AMF under P-sufficient conditions. It is concluded that an adequate P fertilizer and AMF facilitate the production of active medicinal components in P. cuspidatum, associated with expressions of associated genes such as PcCRS1.