Lina Ma

Coordinated Regulation of Arbuscular Mycorrhizal Fungi and Soybean MAPK Pathway Genes Improved Mycorrhizal Soybean Drought Tolerance

Mitogen-activated protein kinase (MAPK) cascades play important roles in the stress response in both plants and microorganisms. The mycorrhizal symbiosis established between arbuscular mycorrhizal fungi (AMF) and plants can enhance plant drought tolerance, which might be closely related to the fungal MAPK response and the molecular dialogue between fungal and soybean MAPK cascades. To verify the above hypothesis, germinal Glomus intraradices (syn. Rhizophagus irregularis) spores and potted experiments were conducted. The results showed that AMF GiMAPKs with high homology with MAPKs from Saccharomyces cerevisiae had different gene expression patterns under different conditions (nitrogen starvation, abscisic acid treatment, and drought). Drought stress upregulated the levels of fungi and soybean MAPK transcripts in mycorrhizal soybean roots, indicating the possibility of a molecular dialogue between the two symbiotic sides of symbiosis and suggesting that they might cooperate to regulate the mycorrhizal soybean drought-stress response. Meanwhile, the changes in hydrogen peroxide, soluble sugar, and proline levels in mycorrhizal soybean as well as in the accelerated exchange of carbon and nitrogen in the symbionts were contributable to drought adaptation of the host plants. Thus, it can be preliminarily inferred that the interactions of MAPK signals on both sides, symbiotic fungus and plant, might regulate the response of symbiosis and, thus, improve the resistance of mycorrhizal soybean to drought stress.

Long-term effect of residue return and fertilization on microbial biomass and community composition of a clay loam soil

A field study was carried out to examine the response of microbial communities of a clay loam soil to long-term (30 years) effects of residue return and fertilization. The experimental design was a split-plot arrangement of treatments, consisting of three residue treatments (crop residues returned at rates of 0, 2500 and 5000 kg/ha) in combination with eight fertilization treatments (control, no fertilizer; N, mineral nitrogen (N) fertilizer; P, mineral phosphorus (P) fertilizer; K, mineral potassium (K) fertilizer; NP, mineral NP fertilizer; NK, mineral NK fertilizer; PK, mineral PK fertilizer; and NPK, mineral NPK fertilizer). Soil microbial communities were characterized by phospholipid fatty acid analysis. Results indicated that the more crop residues were returned, the lower ratio of fungi to bacteria was observed. However, soil microbial biomass was only found to be significantly higher in plots with residues returned at a rate of 5000 kg/ha but not 2500 kg/ha. This suggested there was a threshold for microbial biomass to increase under residue return for the clay loam soil studied. The fertilization effect on soil microbial biomass gradually decreased with increases in the amount of crop residues returned. A significant composition change was observed under N fertilization. Structural equation modelling indicated that soil microbial communities were influenced directly by residue return and indirectly by residue-induced change in ratio of carbon to N and fertilization-induced change in soil pH.

Root-associated bacterial diversities of Oryza rufipogon and Oryza sativa and their influencing environmental factors

Oryza rufipogon is the ancestor of human-cultivated Oryza sativa. However, little is known about the difference between the root-associated microorganisms of O. rufipogon and O. sativa. In this study, the root-associated bacteria of O. rufipogon, Leersia hexandra, and O. sativa from different latitudes in China were studied by DGGE analysis. Their bacterial community structures were compared by principal component analysis. The relationship between root-associated bacteria and soil properties was explored by canonical correspondence analysis. The relationships of glomalin-related soil protein (GRSP) content, soluble sugar content, proline content of the plant, and bacterial diversity indices of their root-associated microorganisms were also investigated. We found both broad-spectrum and host-specific bacteria, and the similarity, diversity and abundance indices of O. rufipogon and L. hexandra were higher than O. sativa root-associated bacteria. However, even living in the same habitat, O. rufipogon and L. hexandra selected different root-associated bacteria. Microbial composition was primarily correlated with available N, P, and K and the annual precipitation. We also found a positive correlation between the soluble sugar content of the plant and GRSP content of the root soil. The above results indicated that the community structure of root-associated bacteria differs between wild rice and cultivated rice. Human activity and the natural selection of the host plants shaped the differences, consistent with our hypothesis.

The effect of Glomus intraradices on the physiological properties of Panax ginseng and on rhizospheric microbial diversity

Background Glomus intraradices is a species of arbuscular mycorrhizal fungi that, as an obligate endomycorrhiza, can form mutually beneficial associations with plants. Panax ginseng is a popular traditional Chinese medicine; however, problems associated with ginseng planting, such as pesticide residues, reduce the ginseng quality. Methods In this experiment, we studied the effect of inoculating G. intraradices on several physiological properties and microbial communities of ginseng. UV-Visible Spectrum method was used to detect physical properties. Denaturing gradient gel electrophoresis method was used to analyze microbial communities. Results The results indicated that inoculation with G. intraradices can improve the colonization rate of lateral ginseng roots, increase the levels of monomeric and total ginsenosides, and improve root activity as well as polyphenol oxidase and catalase activities. We also studied the bacterial and fungal communities in ginseng rhizospheric soil. In our study, G. intraradices inoculation improved the abundance and Shannon diversity of bacteria, whereas fungi showed a reciprocal effect. Furthermore, we found that G. intraradices inoculation might increase some beneficial bacterial species and decreased pathogenic fungi in rhizospheric soil of ginseng. Conclusion Our results showed that G. intraradices can benefit ginseng planting which may have some instructive and practical significance for planting ginseng in farmland.

Fungal communities in ancient peatlands developed from different periods in the Sanjiang Plain, China

Peatlands in the Sanjiang Plain could be more vulnerable to global warming because they are located at the southernmost boundary of northern peatlands. Unlike bacteria, fungi are often overlooked, even though they play important roles in substance circulation in the peatland ecosystems. Accordingly, it is imperative that we deepen our understanding of fungal community structure and diversity in the peatlands. In this study, high-throughput Illumina sequencing was used to study the fungal communities in three fens in the Sanjiang Plain, located at the southern edge of northern peatlands. Peat soil was collected from the three fens which developed during different periods. A total of 463,198 fungal ITS sequences were obtained, and these sequences were classified into at least six phyla, 21 classes, more than 60 orders and over 200 genera. The fungal community structures were distinct in the three sites and were dominated by Ascomycota and Basidiomycota. However, there were no significant differences between these three fens in any α-diversity index (p > 0.05). Soil age and the carbon (C) accumulation rate, as well as total carbon (TC), total nitrogen (TN), C/N ratio, and bulk density were found to be closely related to the abundance of several dominant fungal taxa. We captured a rich fungal community and confirmed that the dominant taxa were those which were frequently detected in other northern peatlands. Soil age and the C accumulation rate were found to play important roles in shaping the fungal community structure.

Rhizospheric fungi and their link with the nitrogen‐fixing Frankia harbored in host plant Hippophae rhamnoides L.

Sea buckthorn (Hippophae rhamnoides L.) is a pioneer plant used for land reclamation and an appropriate material for studying the interactions of symbiotic microorganisms because of its nitrogen‐fixing root nodules and mycorrhiza. We used high‐throughput sequencing to reveal the diversities and community structures of rhizospheric fungi and their link with nitrogen‐fixing Frankia harbored in sea buckthorn collected along an altitude gradient from the Qinghai Tibet Plateau to interior areas. We found that the fungal diversities and compositions varied between different sites. Ascomycota, Basidiomycota, and Zygomycota were the dominant phyla. The distribution of sea buckthorn rhizospheric fungi was driven by both environmental factors and the geographic distance. Among all examined soil characteristics, altitude, AP, and pH were found to have significant (p < 0.05) effect on the rhizospheric fungal community. The rhizospheric fungal communities became more distinct as the distance increased. Moreover, co‐inertia analysis identified significant co‐structures between Frankia and AMF communities in the rhizosphere of sea buckthorn. We conclude that at the large scale, there are certain linkages between nitrogen‐fixing bacteria and the AMF expressed in the distributional pattern.

Community Structure of Rhizomicrobiomes in Four Medicinal Herbs and Its Implication on Growth Management

Medicinal plants are the basic materials of traditional Chinese medicine. Soil characteristics and microbial contribution play important roles in the growth and product quality of medicinal plants, but the link between them in the rhizosphere of medicinal plants has been overlooked. Accordingly, Mentha haplocalyx, Perilla frutescens, Glycyrrhiza uralensis, and Astragalus membranaceus, four plants used in traditional Chinese medicines, were investigated in this study in order to elucidate bacterial and arbuscular mycorrhizal fungal (AMF) diversity in the rhizosphere and its possible association with soil quality. DGGE-based 16S rRNA and 18S rRNA gene sequencing results indicated that the diversity of both bacteria and AMF in Glycyrrhiza uralensis and Astragalus membranaceus was significantly higher than those in Mentha haplocalyx and Perilla frutescens, suggesting that medicinal plants have different preferences even under the same conditions. In addition, enzymatic activities and nutrition were enhanced in the rhizospheric soil of Mentha haplocalyx and Perilla frutescens, and the correlation among AMF diversity, soil enzymatic activities and nutrition was confirmed using RDA analysis. These results suggest the potential to grow medicinal plants with a reasonable rotation or intercrop in order to maintain long-term continuous soil development.

Effect of the biocontrol bacterium Bacillus amyloliquefaciens on the rhizosphere in ginseng plantings

Panax ginseng is an important medicinal herb due to its ability to strengthen the human immune system. However, due to the increasing needs of ginseng in medicine, the continuous cropping of ginseng has become more common and has resulted in increased problems with fungal decay. Thus, chemical fungicides are commonly used in ginseng plantings, which have caused fungicide residue problems. As an alternative control measure, biocontrol bacteria can be used to manage fungal pathogens. Additionally, these bacteria are environmentally friendly and can also improve stress tolerance in plants. In this study, an antifungal bacterial strain, TB6, that possesses ACC deaminase activity was isolated from the rhizosphere of ginseng plants. This strain was identified as Bacillus amyloliquefaciens. TB6 was applied to 2-year-old ginseng seedlings for a 2-year period, and its impact on the soil rhizosphere was evaluated. The results revealed that strain TB6 decreased fungal abundance and diversity; improved urease, catalase, and phosphatase activities; and decreased the cellulase activity of the rhizosphere soil. In addition, strain TB6 also promoted root growth and increased the fresh weight of ginseng roots, in addition to increasing polyphenol oxidase and catalase activities. These results may have practical implications for the use of biocontrol bacteria in ginseng plantings.

Rhizosphere microbiota assemblage associated with wild and cultivated soybeans grown in three types of soil suspensions

ABSTRACT Soil microbial community composition is determined by the soil type and the plant species. By sequencing the V3-V4 region of the bacterial 16S rRNA gene amplicons, the current study assessed the bacterial community assemblage in rhizosphere and bulks soils of wild (Glycine soja) and cultivated (Glycine max) soybeans grown in the suspensions of three important soil types in China, including black, red and soda-saline-alkali soils. The alpha-diversity of the bacterial community in the rhizosphere was significantly higher than that of the bulk soils suggesting that bulk soil lacks plant nurturing effect under the current study conditions. Black and red soils were enriched with nitrifying and nitrogen-fixing bacteria but the soda-saline-alkali soil suspension had more denitrifying bacteria, which may reflect agronomic unsuitability of the latter. We also observed a high abundance of Bradyrhizobium and Pseudomonas, enriched cellulolytic bacteria, as well as a highly connected molecular ecological network in the G. soja rhizosphere soil. Taken all, the current study suggest that wild soybeans may have evolved to recruit beneficial microbes in its rhizosphere that can promote nutrients requisition, biostasis and disease-resistance, therefore ecologically more resilient than cultivated soybeans.

Molecular Communication and Nutrient Transfer of Arbuscular Mycorrhizal Fungi, Symbiotic Nitrogen-Fixing Bacteria, and Host Plant in Tripartite Symbiosis

Plants colonized by Arbuscular mycorrhizal fungi (AMF) greatly enhance Phosphorus (P) and Nitrogen (N) acquisition, especially by extra radical mycelium. On the other hand, soil bacteria referred to as rhizobia establish a symbiotic relationship with legume plants by making novel root organ known as nodules, which fix atmospheric dinitrogen (N2) and transfer it to the host plant. The symbiotic relationship of both AMF and rhizobia with the same host leguminous plants is termed a “tripartite symbiosis”. This tripartite interaction allows legume plants to grow well in nutrient-deficient soils. Sophisticated and complex molecular communication exists between the AMF, rhizobia and host plant during tripartite symbiosis. In this chapter, we focus on some common features of the molecular dialogue shared during tripartite symbiosis. AMF and the nodulation process of rhizobia requires molecular recognition, regulation and specialized complex signaling molecules. For instance, plants secrets strigolactone (SL), which activates and up-regulates the mycorrhizal factor (myc factor) genes of AMF, which make an association with plant root hairs. SL exudates of plant roots also play a crucial role in rhizobial symbiosis, with SL-biosynthesis mutants of Pisum sativum and Lotus japonicus plants showing reduced nodule number. On the other hand, specific flavonoids molecules secreted by legume plants not only trigger the rhizobial nodulation factor (nod factor) genes responsible for nodule formation, but are also vital for hyphal growth of AMF. Moreover, the small polysaccharides, glycoproteins, and proteins (e.g., chitin-related compounds) responsible for stimulating transcription for enzymes involved in the synthesis of flavonoids are considered to be of fungal origin. Thus, establishment of tripartite symbiosis likely requires coordinated gene regulation synchronized by mutual exchange of diffusible signal molecules to induce the expression of genes involved in activation of a common symbiotic pathway and in colonization by microbial symbionts. Another common feature between AMF and rhizobia is that both benefit from carbohydrates provided by the host plant, which uses these symbionts as a source of energy. Finally, after the exchange of common signaling and the establishment of tripartite symbiotic interactions, the genes responsible for P and N metabolism and translocation are up-regulated, which increases the P and N supply to the host plant, especially in nutrient-scarce conditions, and ultimately increases agricultural productivity. However, to date, our knowledge of the synergistic or antagonism effects of the tripartite symbiosis on different beneficial microbes remains sparse, and requires further investigation in future studies.