Abstract:
Plant growth-promoting rhizobacteria (PGPR) can stimulate disease suppression through
the induction of an enhanced state of defense readiness. Here, untargeted ultra-high performance
liquid chromatography–mass spectrometry (UHPLC–MS) and targeted ultra-high performance liquid
chromatography coupled to triple-quadrupole mass spectrometry (UHPLC–QqQ-MS) were used to
investigate metabolic reprogramming in tomato plant tissues in response to priming by Pseudomonas
fluorescens N04 and Paenibacillus alvei T22 against Phytophthora capsici. Roots were treated with the
two PGPR strains prior to stem inoculation with Ph. capsici. Metabolites were methanol-extracted
from roots, stems and leaves at two–eight days post-inoculation. Targeted analysis by UHPLC–QqQMS allowed quantification of aromatic amino acids and phytohormones. For untargeted analysis,
UHPLC–MS data were chemometrically processed to determine signatory biomarkers related to
priming against Ph. capsici. The aromatic amino acid content was differentially reprogrammed in
Ps. fluorescens and Pa. alvei primed plants responding to Ph. capsici. Furthermore, abscisic acid and
methyl salicylic acid were found to be major signaling molecules in the tripartite interaction. LC–
MS metabolomics analysis showed time-dependent metabolic changes in the primed-unchallenged
vs. primed-challenged tissues. The annotated metabolites included phenylpropanoids, benzoic
acids, glycoalkaloids, flavonoids, amino acids, organic acids, as well as oxygenated fatty acids.
Tissue-specific reprogramming across diverse metabolic networks in roots, stems and leaves was also
observed, which demonstrated that PGPR priming resulted in modulation of the defense response to
Ph. capsici infection.
