Abstract:
Pathogenic microorganisms account for large production losses in the agricultural sector.
Phytophthora capsici is an oomycete that causes blight and fruit rot in important crops, especially those
in the Solanaceae family. P. capsici infection is di cult to control due to genetic diversity, arising from
sexual reproduction, and resistant spores that remain dormant in soil. In this study, the metabolomics
of tomato plants responding to infection by P. capsici were investigated. Non-targeted metabolomics,
based on liquid chromatography coupled to mass spectrometry (LC-MS), were used with multivariate
data analyses to investigate time-dependent metabolic reprogramming in the roots, stems, and leaves
of stem-infected plants, over an 8 day period. In addition, phytohormones and amino acids were
determined using quantitative LC-MS. Methyl salicylate and 1-aminocyclopropane-1-carboxylate
were detected as major signalling molecules in the defensive response to P. capsici. As aromatic
amino acid precursors of secondary metabolic pathways, both phenylalanine and tryptophan showed
a continuous increase over time in all tissues, whereas tyrosine peaked at day 4. Non-targeted
metabolomic analysis revealed phenylpropanoids, benzoic acids, glycoalkaloids, flavonoids, amino
acids, organic acids, and fatty acids as the major classes of reprogrammed metabolites. Correlation
analysis showed that metabolites derived from the same pathway, or synthesised by di erent
pathways, could either have a positive or negative correlation. Furthermore, roots, stems, and leaves
showed contrasting time-dependent metabolic reprogramming, possibly related to the biotrophic vs.
necrotrophic life-stages of the pathogen, and overlapping biotic and abiotic stress signaling. As such,
the targeted and untargeted approaches complemented each other, to provide a detailed view of key
time-dependent metabolic changes, occurring in both the asymptomatic and symptomatic stages
of infection.
