Interactions between soil compositions and the wheat root microbiome under drought stress: From an in silico to in planta perspective

As wheat (Triticum aestivum) is an important staple food across the world, preservation of stable yields and increased productivity are major objectives in breeding programs. Drought is a global concern because its adverse impact is expected to be amplified in the future due to the current climate change. Here, we analyzed the effects of edaphic, environmental, and host factors on the wheat root microbiomes collected in soils from six regions in Belgium. Amplicon sequencing analysis of unplanted soil and wheat root endosphere samples indicated that the microbial community variations can be significantly explained by soil pH, microbial biomass, wheat genotype, and soil sodium and iron levels. Under drought stress, the biodiversity in the soil decreased significantly, but increased in the root endosphere community, where specific soil parameters seemingly determine the enrichment of bacterial groups. Indeed, we identified a cluster of drought-enriched bacteria that significantly correlated with soil compositions. Interestingly, integration of a functional analysis further revealed a strong correlation between the same cluster of bacteria and β-glucosidase and osmoprotectant proteins, two functions known to be involved in coping with drought stress. By means of this in silico analysis, we identified amplicon sequence variants (ASVs) that could potentially protect the plant from drought stress and validated them in planta. Yet, ASVs based on 16S rRNA sequencing data did not completely distinguish individual isolates because of their intrinsic short sequences. Our findings support the efforts to maintain stable crop yields under drought conditions through implementation of root microbiome analyses.

Recent advances in actinorhizal symbiosis signaling

Nitrogen and phosphorus availability are frequent limiting factors in plant growth and development. Certain bacteria and fungi form root endosymbiotic relationships with plants enabling them to exploit atmospheric nitrogen and soil phosphorus. The relationships between bacteria and plants include nitrogen-fixing Gram-negative proteobacteria called rhizobia that are able to interact with most leguminous plants (Fabaceae) but also with the non-legume Parasponia (Cannabaceae), and actinobacteria Frankia, which are able to interact with about 260 species collectively called actinorhizal plants. Fungi involved in the relationship with plants include Glomeromycota that form an arbuscular mycorrhizal (AM) association intracellularly within the roots of more than 80% of land plants. Increasing numbers of reports suggest that the rhizobial association with legumes has recycled part of the ancestral program used by most plants to interact with AM fungi. This review focuses on the most recent progress made in plant genetic control of root nodulation that occurs in non-legume actinorhizal plant species.