Wang Ertao's research group and collaborators reveal the co-evolutionary mechanism of arbuscular mycorrhizal symbiosis and nodule symbiosis

Research progress On December 9, 2020, Molecular Plant published online a research paper entitled "Mycorrhizal Symbiosis Modulates the Rhizosphere Microbiota to Promote Rhizobia Legume Symbiosis" completed by Wang Ertao's research group and cooperating team of the Center for Excellence in Molecular Plant Science of the Chinese Academy of Sciences.
Quantitative microbiome, microbial co-occurrence network and microbiota back-joining experiments revealed the interaction mechanism of arbuscular mycorrhizal symbiosis and nodule symbiosis system at the plant rhizosphere level.

The roots of terrestrial plants establish a variety of symbiotic relationships with microorganisms.
For example, more than 80% of terrestrial plants can form a symbiotic relationship with arbuscular mycorrhizal (AM) fungi, among which legumes can also form rhizobia Symbiotic nitrogen fixation relationship.

AM symbiosis and root nodule symbiosis can synergistically promote plant growth by improving the ability of plants to obtain phosphorus and nitrogen.

As an important part of terrestrial ecosystem, AM fungus is a key link of ecosystem carbon cycle.

In addition, AM fungi connect plants underground through mycelial network, forming a huge network and affecting the diversity of plants.

The establishment of symbiosis between plant roots and microorganisms is a long-term co-evolution process.

Arbuscular mycorrhizal symbiosis was formed 460 million years ago, and its symbiosis signal pathway was further used by legumes to participate in the establishment of the symbiosis between legumes and nitrogen-fixing rhizobia.

However, we know little about the interaction and co-evolution of AM fungi and rhizobia in terrestrial ecosystems.

Co-evolution between organisms depends on interaction, especially cooperation and competition between organisms.

The area around the root is called the rhizosphere, and this microenvironment represents the main niche of plant-microbe and microbe-microbe interactions.

The rhizosphere microbiome of plants is known as the second genome of plants, which is essential for plant growth and environmental adaptation.

Traditional rhizosphere microbiome research mainly uses high-throughput sequencing of bacterial 16S rRNA genes or fungal ribosomal DNA internal transcribed spacers (ITS) sequences to assess the relative abundance of microbial populations, but this method cannot provide samples The absolute abundance of medium microorganisms hinders the study of interactions between transboundary microorganisms (such as AM fungi and rhizobia).

Based on quantitative microbiota profiling (QMP) in the early stage of the laboratory, it was found that the number of bacteria in the rhizosphere soil was nearly 10 times that of the root soil, and the absolute abundance of the main bacteria in the rhizosphere soil was significantly expanded.
Based on this, we propose a new model for the assembly of rhizosphere microbiota (An amplification-selection model for quantified rhizosphere microbiota assembly, Science Bulletin, 2020).

The research planted wild-type Medicago truncatula and mutants with AM symbiosis and/or nodule symbiosis defect under natural soil conditions, and studied the bacterial and microbial content in rhizosphere and root samples through 16S rRNA gene high-throughput sequencing and microbiota quantification.
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The study found that the mycorrhizal symbiosis defect significantly reduced the bacterial microbiota—especially Rhizobiales—proliferation in the plant rhizosphere and changed the population structure of the rhizosphere and the microbiome within the root.

Based on the analysis of the microbial co-occurrence network, it was found that Rhizobium bacteria are at the core of the plant rhizosphere with normal mycorrhizal symbiosis.
The lack of mycorrhizal symbiosis affects the stability of the network. The study further studied the interaction between AM symbiosis and nodule symbiosis in the rhizosphere microenvironment through high-throughput sequencing and microbiota quantitative analysis of the rhizobia rpoB gene and AM fungal SSU rRNA gene, and found that AM symbiosis can promote a variety of symbiotic nodules The proliferation of bacterial populations in the rhizosphere.

Finally, the research of rhizosphere microbial community back-joining showed that the microbial community affected by AM symbiosis can promote the nodulation of different legumes in natural soil.

The study shows that the establishment of the symbiosis relationship between legumes and rhizobia is the result of the interaction of plant-rhizobium-environment.
The huge hyphae network of AM fungi provides nutrients to plants and also helps plant roots to accumulate nodules.
Bacteria, promote the symbiosis of legumes and rhizobia.

This study revealed the co-evolution of arbuscular mycorrhizal symbiosis and nodule symbiosis in the process of plants adapting to the terrestrial environment from the rhizosphere level.

Figure Wang Ertao's research portfolio.
This work was completed by Wang Ertao's research group from the Center for Excellence in Molecular Plant Science, Chinese Academy of Sciences, Liu Huan's research group at the Institute of Life Sciences of Shenzhen BGI and Zhang Xuebin's research group from Henan University.
Dr.
Wang Xiaolin is the first author of the paper, Wang Ertao Researcher and senior engineer Liu Huan and Professor Zhang Xuebin are the co-corresponding authors of the paper.

The research was funded by the Chinese Academy of Sciences, the National Natural Science Foundation of China, and the National Gene Bank.

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