Microbes living in close association with plant roots can greatly expand the plant’s metabolic capabilities. For example, plant-associated microbes enhance plant protection against biotic and abiotic stresses by inducing immunity and/or enhancing nutrient acquisition. Since sorghum is an important staple crop, it is of key importance to advance our understanding of the sorghum root-associated microbiomes to further explore their functional capabilities. The study “Back to the roots: defining the core microbiome of Sorghum bicolor in agricultural field soils from the centre of origin” in FEMS Microbiology Ecology explores the bacterial taxa in the sorghum rhizosphere. Francisco Dini-Andreote explains for the #FEMSmicroBlog how the “back-to-the-roots” approach helped identify key sorghum-associated bacteria. #FascinatingMicrobes
Factors structuring the rhizosphere-associated microbiomes
The plant rhizosphere is broadly defined as the zone of the soil surrounding plant roots. Plants actively enrich and select for specific microbial taxa by excreting signal molecules and producing mucous molecules, cell wall materials and lysates. Together, these molecules cause local changes in the concentration of certain nutrients, O2 and pH around the root with direct impacts on microbial cell metabolism and activity.
Many factors influence the assembly and functioning of plant rhizosphere microbiomes. These generally include the initial composition of the bulk soil microbiome, soil physicochemical parameters, like nutrient content, pH, soil texture and salinity, as well as the genotype, nutritional need and developmental stage of the plant.
The back-to-the-roots approach
The study “Back to the roots: defining the core microbiome of Sorghum bicolor in agricultural field soils from the centre of origin” in FEMS Microbiology Ecology used the novel “back-to-the-roots” approach to look at microbiomes of different sorghum plant genotypes. These included ancestor sorghum genotypes – or the wild types – as well as several other sorghum domesticated and commercial varieties obtained at the centre of origin. The geographic location where sorghum first originated was Ethiopia.
This approach assumed that wild plant ancestors cultivated in soils from their center of origin have evolved interactions with specific beneficial microbial taxa. Such interactions would then differ from those of modern crops cultivated in intensive agricultural soils.
As such, the study combines soil survey analysis, as the collection of soils obtained in an area of approximately 40,000 square kilometer, with plant-microbe interaction microcosm experimentation. The aim was to link specific plant genotypes to the composition of rhizosphere microbiomes. Based on these data, potential core microbiome taxa consistently occurring across all samples and soil-genotype combinations were explored.
Linking sorghum genotypes to rhizosphere microbiomes
So far, research efforts aimed at identifying how specific plant genotypes select and enrich for specific microbial taxa in the rhizosphere. Similarly, wild progenitors of modern crops have potential traits and genotypic or phenotypic characteristics that may trigger the assembly and function of beneficial microbial taxa in the plant root.
The article explores this idea by combining the genomic analysis of a set of sorghum genotypes with the assessment of the composition of root-associated microbiomes across distinct soils from the center of origin of sorghum. The results show that in some soils, wild genotypes tend to select similar rhizosphere microbial taxa. And interestingly, this correlation varies across distinct soils, which indicates that depending on the soil type, different plant genotypes select for specific microbial taxa.
In addition, this study was able to enumerate a set of taxa consistently found across plant-soil combinations –the “core microbiome of sorghum”. Future studies will focus on isolating and exploring the potential beneficial functions of this core microbiome.
In this sense, particularly in Sub-Saharan Africa, sorghum crops have been largely impacted by the parasitic weed Striga as seen in the figure. Exploring the genetic and metabolic capabilities of sorghum-associated microbiomes in potentially controlling the impact of this parasite weed represents an innovative strategy to promote plant protection in a sustainable manner.
- Read the article “Back to the roots: defining the core microbiome of Sorghum bicolor in agricultural field soils from the centre of origin” by Abera et al. (2022).
Francisco Dini-Andreote is an Assistant Professor in the Department of Plant Science at the Pennsylvania State University (USA). He obtained a Ph.D. at the University of Groningen (The Netherlands) and worked as a postdoctoral researcher at The Netherlands Institute of Ecology (NIOO-KNAW). He is currently an Editorial board member of The ISME Journal and an Associate Editor of Frontiers in Microbiology. His lab researches microbial communities living in soils and in association with plants. His work largely focuses on exploring the diversity and functioning of microbial communities, identifying the ecological and evolutionary processes mediating community assembly, and examining the mechanisms by which microorganisms mitigate plant biotic and abiotic stresses.
About this blog section
The section #FascinatingMicrobes for the #FEMSmicroBlog explains the science behind a paper and highlights the significance and broader context of a recent finding. One of the main goals is to share the fascinating spectrum of microbes across all fields of microbiology.
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