The Metabolic Response of Brachypodium Roots to the Interaction with Beneficial Bacteria Is Affected by the Plant Nutritional Status

Abstract

The potential of plant growth promoting (PGP) bacteria in improving the performance of plants in suboptimal environments is increasingly acknowledged, but little information is available on the mechanisms underlying this interaction, particularly when plants are subjected to a combination of stresses. In this study, we investigated the effects of the inoculation with the PGP bacteria Azospirillum brasilense (Azospirillum) on the metabolism of the model cereal Brachypodium distachyon (Brachypodium) grown at low temperatures and supplied with insufficient phosphorus. Investigating polar metabolite and lipid fluctuations during early plant development, we found that the bacteria initially elicited a defense response in Brachypodium roots, while at later stages Azospirillum reduced the stress caused by phosphorus deficiency and improved root development of inoculated plants, particularly by stimulating the growth of branch roots. We propose that the interaction of the plant with Azospirillum was influenced by its nutritional status: bacteria were sensed as pathogens while plants were still phosphorus sufficient, but the interaction became increasingly beneficial for the plants as their phosphorus levels decreased. Our results provide new insights on the dynamics of the cereal-PGP bacteria interaction, and contribute to our understanding of the role of beneficial microorganisms in the growth of cereal crops in suboptimal environments.

The effect of phosphate application in Pb-contaminated soil on the oxidative stress of leaves, Pb accumulation in biomass of maize and Pb speciation in rhizosphere soil

“…This result indicates that the application of chemical fertilizers in soil not only increases the content of ionic P in maize rhizosphere soil, but also transforms the chemically mobilized P (such as O-P, Ca-P) into the ionic state due to the decrease of soil pH. In this process, although mobilized P is conducive to plant absorption (Schillaci et al 2021;Istenič and Božič 2021;Pedro et al 2021;Suresh et al 2021), and can also increase the risk of soil phosphorus loss with surface runoff (Boero 1977;Li et al 2013;Temporetti et al 2019). Some studies have shown that the organic acids exuded by plant roots reduce the pH of the rhizosphere soil and promotes the release of ionic P. And with the decrease of H + and organic acid in the soil, the insoluble phosphorus compounds (such as calcium phosphate compounds, hydroxy aluminum phosphate (iron) compounds) in the soil are hydrolyzed and dissociated into H2PO4 -, HPO4 2and other ionic states ( (Hayes et al 2000;Boafo et al 2018).…”

Metabolomics as an emerging tool to study plant–microbe interactions

“…The sole comparison with the metabolome of plants and microorganisms grown in axenic culture can provide some useful information, but does not give the full picture, as there still can be compounds produced by an organism only when interacting with another. Integrating metabolomics with the analysis of the transcriptome of plants and microorganisms alone and interacting with each other can help in this task by ascribing the various metabolites to the organism which also show an increased expression of the genes related to their metabolism [38]. • As mentioned above, there has been little or no effort made in differentiating microbial metabolites from plant metabolites as the microbes are not removed from the metabolite extraction [47,48,49,50].…”

“…For example, metabolomics techniques such as untargeted GC–MS and untargeted QqTOF LC–MS were used to compare the root metabolic and lipid profiles of inoculated and non-inoculated Brachypodium distachyon Bd21–3 plants with Azospirillum brasilense Sp245 grown at low temperatures and supplied with insufficient phosphorus. It has been proposed that the nutritional status of the plant influenced the interaction of the plant with Azospirillum: bacteria were sensed as pathogens despite sufficient phosphorus in plants, however, the interaction became beneficial for the plants as their phosphorus levels decreased [ 38 ]. Another study by Gupta et al [ 39 ] used GC–MS to analyse polar metabolites and LC–MS to analyse lipids in roots of two barley cultivars (with contrasting salinity tolerance) during the early stages of interaction with Trichoderma harzianum T-22.…”

MicroRNA Mediated Plant Responses to Nutrient Stress

“…This is rapidly becoming the most serious environmental stress, which has a negative impact on normal growth and development [ 3 ]. According to researchers, plants have evolved efficient mechanisms to observe their nutritional status and adapt to variations in nutrient concentrations [ 4 , 5 , 6 ]. With the success of the genome sequencing of plants and through the development of new genomic tools, several regulatory elements have been identified as being involved in plant responses to nutritional stress [ 7 , 8 ].…”