The plant nutrition team of the Institute of Agricultural Resources and Regional Planning (IARRP) of the Chinese Academy of Agricultural Sciences (CAAS) discovered a highly conserved core bacterial microbiome with nitrogen-fixing ability that colonizes maize xylem sap, which provides nitrogen for maize and promotes root growth.

The related research results were published in Nature Communications.

Similar to the human microbiome, the plant microbiome is called the second genome of plants and is crucial for plant growth and development, nutrient absorption, and resistance to pests and diseases. The mucilage of the aerial roots of some maize landraces in poor Mexican soils is rich in the nitrogen-fixing bacteria that contribute 29-82% of maize nitrogen nutrition through biological nitrogen fixation. Therefore, the in-depth utilization of crop-microbe interactions is crucial for future sustainable agricultural development.

In recent years, a large number of studies have focused on the structure and function of microbial communities at key interfaces such as the plant rhizosphere and phyllosphere. However, other parts of the plant, such as the stem vascular tissue, core microbial community composition and their possible important functions in host health have been overlooked.

By evaluating the assembly mechanism and function of the maize microbiome across different soil types, climate zones and genotypes, this study found that maize stem xylem selectively recruits a highly conserved core microbial community dominated by Gammaproteobacteria, and identified 25 core bacterial taxa consisting of partially efficient nitrogen-fixing bacteria and other auxiliary bacteria.

On this basis, the study established a synthetic community (SynComs) composed of two core nitrogen-fixing bacteria and two auxiliary bacteria, GFP-labeled strains and an N isotope dilution method to confirm the lifestyle and nitrogen-fixing ability of SynComs plants in vivo, by which they achieved biological nitrogen fixation that contributed 11.8% of total nitrogen in maize stems. SynComs also increased root biomass, suggesting a multi-mechanism synergy between the core endophyte and the host. The xylem vessel microbiome represents a neglected class of important plant functional "gut" bacteria that play a key role in nitrogen fixation and growth promotion in crops.

Zhang Liyu, a doctoral student from the IARRP, is the first author of this article, associate researcher Ai Chao and Laurent Philippot of the French Academy of Agricultural Sciences are the co-corresponding authors, and the chief scientist of the research team is academician Zhou Wei. This research was funded by the Youth Support Program of the China Association for Science and Technology and the Innovation Project of the Chinese Academy of Agricultural Sciences.

Paper link: https://doi.org/10.1038/s41467-022-31113-w