I'll be there for you: Microbe-mediated resilience to abiotic stress in Sorghum bicolor

Elle Barnes, DOE Joint Genome Institute, Berkeley National Lab, Berkeley, CA, Dawn Chiniquy, Environmental Genomics and Systems Biology, Berkeley National Lab, Kyle Hartman, DOE Joint Genome Institute, Berkeley National Lab and Susannah G. Tringe, DOE Joint Genome Institute, Berkeley National Laboratory, Berkeley, CA

Background/Question/Methods
Sorghum bicolor is a genetically diverse crop cultivated for a variety of agronomic uses, including grain, sugar, and energy production. However, cultivation of energy sorghum for biofuel production will require the use of marginal lands with potentially low nutrient availability and/or periods of water stress. All plants growing in soil harbor diverse communities of microbes that inhabit the areas in, on, and around their roots. Selected members of these microbial communities can provide benefits to their plant hosts, including direct growth promotion and conferring tolerances to abiotic and biotic stress. To explore a possible microbial solution to increase the nutrient use efficiency and resilience to water stress in sorghum, we used 16S rRNA sequencing, metagenomics, and SPIEC-EASI network analysis to survey the diversity, structure, and functional potential of sorghum bacterial communities. We report how drought, nitrogen deficiency, and plant genotype alter the sorghum microbiome throughout the growing season and correlate these changes with sorghum biomass.
Results/Conclusions
We found a significant effect of growing condition (N and water availability) on the alpha and beta diversity of the sorghum rhizosphere. However, the strength of the effect was dependent on sorghum genotype and location within the field. In addition to affecting microbial diversity and composition, network analysis suggested that growth condition also influenced the structure and co-associations of specific beneficial bacterial taxa. We subset the rhizosphere to focus on bacterial taxa identified as putatively plant growth promoting (PGPB). We found that sorghum dry weight and height were positively correlated with the relative abundance of PGPB, regardless of genotype or growth condition. However, the composition of PGPB varied by treatment. Additionally, abiotic stressed plants showed increases over time in the abundance of bacterial orthologous groups associated with root elongation, nitrogen fixation, siderophore biosynthesis, and plant hormone biosynthesis. Overall, our results suggest that under abiotic stress, sorghum individuals are able to recruit beneficial bacteria to their rhizosphere and that microbe-mediated interactions play a critical role in plant resilience.