Targeted and Untargeted Metabolomic Analyses Reveal Organ Specificity of Specialized Metabolites in the Model Grass Brachypodium distachyon.

Brachypodium distachyon, because of its fully sequenced genome, is frequently used as a model grass species. However, its metabolome, which constitutes an indispensable element of complex biological systems, remains poorly characterized. In this study, we conducted comprehensive, liquid chromatography-mass spectrometry (LC-MS)-based metabolomic examination of roots, leaves and spikes of Brachypodium Bd21 and Bd3-1 lines. Our pathway enrichment analysis emphasised the accumulation of specialized metabolites representing the flavonoid biosynthetic pathway in parallel with processes related to nucleotide, sugar and amino acid metabolism. Similarities in metabolite profiles between both lines were relatively high in roots and leaves while spikes showed higher metabolic variance within both accessions. In roots, differences between Bd21 and Bd3-1 lines were manifested primarily in diterpenoid metabolism, while differences within spikes and leaves concerned nucleotide metabolism and nitrogen management. Additionally, sulphate-containing metabolites differentiated Bd21 and Bd3-1 lines in spikes. Structural analysis based on MS fragmentation spectra enabled identification of 93 specialized metabolites. Among them phenylpropanoids and flavonoids derivatives were mainly determined. As compared with closely related barley and wheat species, metabolic profile of Brachypodium is characterized with presence of threonate derivatives of hydroxycinnamic acids.

Secondary metabolites in plant innate immunity: conserved function of divergent chemicals.

Plant secondary metabolites carry out numerous functions in interactions between plants and a broad range of other organisms. Experimental evidence strongly supports the indispensable contribution of many constitutive and pathogen-inducible phytochemicals to plant innate immunity. Extensive studies on model plant species, particularly Arabidopsis thaliana, have brought significant advances in our understanding of the molecular mechanisms underpinning pathogen-triggered biosynthesis and activation of defensive secondary metabolites. However, despite the proven significance of secondary metabolites in plant response to pathogenic microorganisms, little is known about the precise mechanisms underlying their contribution to plant immunity. This insufficiency concerns information on the dynamics of cellular and subcellular localization of defensive phytochemicals during the encounters with microbial pathogens and precise knowledge on their mode of action. As many secondary metabolites are characterized by their in vitro antimicrobial activity, these compounds were commonly considered to function in plant defense as in planta antibiotics. Strikingly, recent experimental evidence suggests that at least some of these compounds alternatively may be involved in controlling several immune responses that are evolutionarily conserved in the plant kingdom, including callose deposition and programmed cell death.