Effects of Arbuscular Mycorrhizal Fungi on the Physiology and Saponin Synthesis of Paris polyphylla var. yunnanensis at Different Nitrogen Levels

Arbuscular mycorrhizal fungi(AMF)are important members of the plant microbiome and affect the uptake and transfer of mineral elements by forming a symbiotic relationship with plant roots.Nitrogen(N),as an important min­eral element,can directly affect plant growth and development at different N levels.It has been confirmed that inoc­ulation with AMF can improve the efficiency of N utilization by plants.However,there are still fewer reports on the dynamic relationship between arbuscular mycorrhizal and plant secondary metabolites at different nitrogen levels.In this experiment,the physiological indexes and genes related to saponin synthesis were determined by applying differ­ent concentration gradients of nitrogen to the medicinal plant P.polyphylla var.yunnanensis infested by AMF as the test material.It was found that nitrogen addition increased the biomass,chlorophyll content,and nutrient content of above-and below-ground plant parts and increased the content of saponin content of P.polyphylla var.yunnanensis to some extent,but AMF inoculation increased the saponin content of P.polyphylla var.yunnanensis more significantly.AMF inoculation also promoted the expression of genes related to the saponin synthesis pathway,including 3-hy­droxy-3-methylglutaryl coenzyme A synthase(HMGS),squalene epoxidase 1(SE1),and cycloartenol synthase(CAS),which is in according with the accumulation of saponin in plants.It also may increase the saponin content of AMF plants by altering the expression of P450s and UGTs related to saponin synthesis.

Arbuscular mycorrhiza and plant growth promoting endophytes facilitates accumulation of saponin under moderate drought stress

Objective: Paris polyphylla var. yunnanensis, one of the important medicinal plant resources in Yunnan,China, usually takes 6–8 years to be harvested. Therefore, it is urgent to find a method that can not only shorten its growth years, but also improve its quality. In this study, we examined the effects of a combination treatment of arbuscular mycorrhizal fungi(AMF) and plant growth-promoting endophytes(PGPE)and drought stress on the accumulation of saponins in it.Methods: P. polyphylla var. yunnanensis was infected with a mixture of AMF and PGPE under drought stress. The content of saponins, as well as morphological, physiological, and biochemical indicators, were all measured. The UGTs gene related to saponin synthesis was obtained from transcriptome data by homologous comparison, which were used for RT-PCR and phylogenetic analysis.Results: Regardless of water, AMF treatment could infect the roots of P. polyphylla var. yunnanensis, however double inoculation with AMF and PGPE(AMF + PGPE) would reduce the infection rate of AMF. Plant height, aboveground and underground fresh weight did not differ significantly between the single inoculation AMF and the double inoculation treatment under different water conditions, but the inoculation treatment significantly increased the plant height of P. polyphylla var. yunnanensis compared to the noninoculation treatment. Single inoculation with AMF considerably increased the net photosynthetic rate,stomatal conductance, and transpiration rate of P. polyphylla var. yunnanensis leaves under various water conditions, but double inoculation with AMF + PGPE greatly increased the intercellular CO2concentration and chlorophyll fluorescence parameter(Fv/Fm). Under diverse water treatments, single inoculation AMF had the highest proline content, whereas double inoculation AMF + PGPE may greatly improve the amount of abscisic acid(ABA) and indoleacetic acid(IAA) compared to normal water under moderate drought. Double inoculation AMF + PGPE treatment improved the proportion of N, P, and K in the rhizome of P. polyphylla var. yunnanensis under various water conditions. Under moderate drought stress,AMF + PGPE significantly enhanced the contents of P. polyphylla var. yunnanensis saponins I, II, VII, and total saponins as compared to normal water circumstances. Farnesyl diphosphate synthase(FPPS),Geranyl pyrophosphate synthase(GPPS), Cycloartenol synthase(CAS), and Squalene epoxidase(SE1) were the genes that were significantly up-regulated at the same time. The amount of saponins was favorably linked with the expression of CAS, GPPS, and SE1. Saponin VI content and glycosyl transferase(UGT)010922 gene expression were found to be substantially associated, as was saponin II content and UGT010935 gene expression.Conclusion: Under moderate drought, AMF + PGPE was more conducive to the increase of hormone content, nutrient absorption, and total saponin content in P. polyphylla var. yunnanensis, and AMF + PGPE could up regulate the expression of key genes and UGTs genes in one or more steroidal saponin synthesis pathways to varying degrees, thereby stimulating the synthesis and accumulation of steroidal saponins in the rhizome of P. polyphylla var. yunnanensis. The combination of AMF and PGPE inoculation, as well as adequate soil drought, reduced the buildup of saponins in P. polyphylla var. yunnanensis and increased its quality.

Integrated analysis of changes in soil microbiota and metabolites following long-term fertilization in a subtropical maize-wheat agroecosystem

Although the application of inorganic fertilizer is a widespread agronomic practice used to boost soil productivity and crop yields,the effects on soil microbiome and the metabolic mechanisms involved in the high-yield response of crops to long-term fertilization remain poorly described.In this study,combined metagenomic and metabolomic analyses were used to explore the mechanism of crop yield response to the 20-year application of nitrogen-phosphorus-potassium fertilizers in a subtropical agroecosystem in Southwest China.Soil bacterial and fungal communities were monitored using16S r RNA(bacteria)and internal transcribed spacer 1(ITS1)full-length gene(fungi)amplicon sequencing technologies,and metabolites were detected using a liquid chromatograph mass spectrometer.The results revealed that,in addition to providing nutrients,long-term fertilization shaped the compositions of bacteria and fungi to increase crop yields.Long-term fertilization significantly increased the relative abundances of plant growth-promoting rhizobacteria and arbuscular mycorrhizal fungi and promoted the secretion of soil metabolites such as carbohydrates,organic acids,and organic nitrogen compounds,which were primarily enriched in amino acid metabolism pathways.The increases in carbon and nitrogen sources and bioactive substances in soil promoted the increases in plant biomass and thereby maintained soil quality and production capacity.The findings highlighted the importance of soil metabolites in maintaining soil productivity as well as crop yields,and suggested that regulating key metabolites could increase crop yields in agroecosystems.