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Metabolomic Variation Aligns with Two Geographically Distinct Subpopulations of Brachypodium Distachyon before and after Drought Stress.

ABSTRACT: Brachypodium distachyon (Brachypodium) is a non-domesticated model grass that has been used to assess population level genomic variation. We have previously established a collection of 55 Brachypodium accessions that were sampled to reflect five different climatic regions of Turkey; designated 1a, 1c, 2, 3 and 4. Genomic and methylomic variation differentiated the collection into two subpopulations designated as coastal and central (respectively from regions 1a, 1c and the other from 2, 3 and 4) which were linked to environmental variables such as relative precipitation. Here, we assessed how far genomic variation would be reflected in the metabolomes and if this could be linked to an adaptive trait. Metabolites were extracted from eight-week-old seedlings from each accession and assessed using flow infusion high-resolution mass spectrometry (FIE-HRMS). Principal Component Analysis (PCA) of the derived metabolomes differentiated between samples from coastal and central subpopulations. The major sources of variation between seedling from the coastal and central subpopulations were identified. The central subpopulation was typified by significant increases in alanine, aspartate and glutamate metabolism and the tricarboxylic acid (TCA) cycle. Coastal subpopulation exhibited elevated levels of the auxin, indolacetic acid and rhamnose. The metabolomes of the seedling were also determined following the imposition of drought stress for seven days. The central subpopulation exhibited a metabolomic shift in response to drought, but no significant changes were seen in the coastal one. The drought responses in the central subpopulation were typified by changes in amino acids, increasing the glutamine that could be functioning as a stress signal. There were also changes in sugars that were likely to be an osmotic counter to drought, and changes in bioenergetic metabolism. These data indicate that genomic variation in our Turkish Brachypodium collection is largely reflected as distinctive metabolomes ("metabolotypes") through which drought tolerance might be mediated.

SUBMITTER: Skalska A

PROVIDER: S-EPMC8003576 | biostudies-literature |

REPOSITORIES: biostudies-literature

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Project description:Brachypodium distachyon as an annual species that colonises broken ground is a highly appropriate model to define drought tolerance mechanisms. We have previously identified accessions exhibiting drought tolerance, high susceptibility and intermediate tolerance to drought; respectively, ABR8, KOZ1 and ABR4, from a screen of 138 genotypes. To define the mechanisms of tolerance, the responses to drought were assessed using transcriptomic and metabolomic approaches. Analysis of RNA-seq before and following drought suggested relatively few differentially expressed genes in ABR8. Linking these to gene ontology (GO) terms revealed an enrichment for biological processes related to “regulated stress response”, “plant cell wall” and “oxidative stress”. Interestingly, drought tolerance also appeared to correlate with pre-existing differences in gene expression linked to GO terms associated with the cell wall. These included glycoside hydrolases involved in cell wall remodelling, pectin methylesterases, expansins and a pectin acetylesterase. Metabolomic assessments of the same samples also indicated few statistically significant changes in ABR8 with drought. Instead, pre-existing differences in the cell-wall associated metabolites appeared to correlate with drought tolerance. Our data suggests two different modes/levels at which cell wall characteristics can play a role in conferring drought tolerance: (i) an active response mode/level which involves stress induced changes in cell wall features to help the plant cope with drought and (ii) an intrinsic mode in which innate differences in cell wall composition and architecture between genotypes are important in determining tolerance to drought stress. Both modes seem to contribute to the drought tolerance of ABR8. Identification of the exact mechanisms through which the cell wall confers drought tolerance will be important to fully exploit the contribution of the cell wall in the development of drought tolerant cereals and other grasses.

Project description:Drought is an important environmental stress limiting the productivity of major crops worldwide. Understanding drought tolerance and possible mechanisms for improving drought resistance is therefore a prerequisite to develop drought-tolerant crops that produce significant yields with reduced amounts of water. Brachypodium distachyon (Brachypodium) is a key model species for cereals, forage grasses, and energy grasses. In this study, initial screening of a Brachypodium germplasm collection consisting of 138 different ecotypes exposed to progressive drought, highlighted the natural variation in morphology, biomass accumulation, and responses to drought stress. A core set of ten ecotypes, classified as being either tolerant, susceptible or intermediate, in response to drought stress, were exposed to mild or severe (respectively, 15 and 0% soil water content) drought stress and phenomic parameters linked to growth and color changes were assessed. When exposed to severe drought stress, phenotypic data and metabolite profiling combined with multivariate analysis revealed a remarkable consistency in separating the selected ecotypes into their different pre-defined drought tolerance groups. Increases in several metabolites, including for the phytohormones jasmonic acid and salicylic acid, and TCA-cycle intermediates, were positively correlated with biomass yield and with reduced yellow pixel counts; suggestive of delayed senescence, both key target traits for crop improvement to drought stress. While metabolite analysis also separated ecotypes into the distinct tolerance groupings after exposure to mild drought stress, similar analysis of the phenotypic data failed to do so, confirming the value of metabolomics to investigate early responses to drought stress. The results highlight the potential of combining the analyses of phenotypic and metabolic responses to identify key mechanisms and markers associated with drought tolerance in both the Brachypodium model plant as well as agronomically important crops.

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Metabolomic Variation Aligns with Two Geographically Distinct Subpopulations of Brachypodium Distachyon before and after Drought Stress.

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