Temporal metabolic profiling of the Quercus suber-phytophthora cinnamomi system by middle-infrared spectroscopy

The oomycete Phytophthora cinnamomi is an aggressive plant pathogen, detrimental to many ecosystems including cork oak (Quercus suber) stands, and can inflict great losses in one of the greatest hotspots' for biodiversity in the world. Here, we applied Fourier transform-infrared (FT-IR) spectroscopy combined with chemometrics to disclose the metabolic patterns of cork oak roots and P.cinnamomi mycelium during the early hours of the interaction. As early as 2h post-inoculation (hpi), cork oak roots showed altered metabolic patterns with significant variations for regions associated with carbohydrate, glycoconjugate and lipid groups when compared to mock-inoculated plants. These variations were further extended at 8hpi. Surprisingly, at 16hpi, the metabolic changes in inoculated and mock-inoculated plants were similar, and at 24hpi, the metabolic patterns of the regions mentioned above were inverted when compared to samples collected at 8hpi. Principal component analysis of the FT-IR spectra confirmed that the metabolic patterns of inoculated cork oak roots could be readily distinguished from those of mock-inoculated plants at 2, 8 and 24hpi, but not at 16hpi. FT-IR spectral analysis from mycelium of P.cinnamomi exposed to cork oak root exudates revealed contrasting variations for regions associated with protein groups at 16 and 24h post-exposure (hpe), whereas carbohydrate and glycoconjugate groups varied mainly at 24hpe. Our results revealed early alterations in the metabolic patterns of the host plant when interacting with the biotrophic pathogen. In addition, the FT-IR technique can be successfully applied to discriminate infected cork oak plants from mock-inoculated plants, although these differences were dynamic with time. To a lesser extent, the metabolic patterns of P.cinnamomi were also altered when exposed to cork oak root exudates