| Arbuscular mycorrhizal (AM) fungi can form symbiotic associations with the majority of terrestrial higher plants, which is probably one of the most widespread symbioses on earth. Many studies have shown that AM symbioses influence mineral nutrition, water uptake, growth and development of the host plants, and play a significant role in plant response to environmental stresses, such as drought, high temperature, heavy metal pollution, etc. However, most research focused on the physiological and ecological function of host plants as affected by AMFs. To the best of our knowledge, the mechanism underlying AM symbiotic crosstalk, especially the signaling between AM fungi and plants in response to environmental stresses, have not been clearly described. In this study, we took Zea mays (B73) as host plant to investigate the effect of the AM fungi exudates on the responses of AM associations to phosphorus stress, to provide the basis of mechanism research of active molecules in AM fungal exudates. The main results are as follows:(1) The effect of AM fungi exudates on the basic metabolism of Zea mays Taking germinated spores exudates (GSE) as AM fungi exudates, in the condition of adding GSE, we used genome and metabolism analysis technology to investigate the effect of AM fungi exudates on the plants basic metabolism. The results of gene-chip array revealed that compared with 6h control, there was no significant changes in gene expression under the GSE treatment for 6h. In contrast, treatment for 24h significantly affected genes expression in maize roots, the genes affected were mainly involved in the metabolism of amino acid, glucose, fatty acid and signal transduction. The metabolome data also showed that 6h treatment had no significant effect on metabolome of maize roots, while significant changes metabolite contents were also found under GSE treatment for 24h. The relative content of metabolites relavant to amino acid, sugar, and fatty acid metabolism had increased as well as uracil putrescine, and spermine, etc. Our studyproved that AM fungi exudates had a positive significant impact on carbon and nitrogen metabolism including gene expression and metabolite contents, indicating that host plant rapidly respond to AM fungal signal molecules and getting ready for AM fungal infection(2) The role of AM fungi exudates in the plants response to phosphorus stress In a compartment culture system, with or without AM fungi exudates treatment were arranged, taking inoculation compartment as the source of AM fungi exudates that can diffuse freely between compartments through the mieroporous membrane. Real-time PCR analysis was performed to investigate the expression of genes related to carbon and phosphorus metabolism in maize roots induced by fungal exudates under different phosphorus (P) supplies. The results indicated that, as for AM symbionts. AM fungi colonization increased maize dry weight, P concentration, related genes expression of carbon and phosphorus metabolism in AM fungi and maize. However, in the treatment of AM exudates and P, under high P (100 mg kg-1) condition, plant dry weight, and phosphorus content of plant were significantly higher than control, but no changes of those in AM fungi exudates treatment. Moreover, the up-regulated genes expressions of related to carbon and phosphorus cycling were found in AM fungi exudates treatment under low P condition. Besides, they increased along with the time. However, AM fungi exudates that influenced gene expression were not prominent in the condition of high P supplies. Our study proved that AM fiingi exudates could regulate gene expression in a higher level and stimulate response to AM infection of plants under low P stress. Compared with high P stress, the regulation role of AM fungi exudates seemed more obvious under low P stress, in some intent, which supported that AM symbiosis may be more important for host plants to defense P starvation. |
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