PA pre-treatment primes the accumulation of phenylpropanoid pathway products in nematode-infected roots
To further investigate the effect of PA treatment on the PPP, tomato seedlings were mock- or PA-treated and then either mock-inoculated or inoculated with M. incognita 24 hours later. Free and cell-wall bound phenolic substances as well as lignin were quantified in leaves, stems and roots seven dai. M. incognita infection in PA-treated plants led to a significant increase in the abundance of free phenolic compounds (+25%, P = 0.013), cell wall-bound phenolic compounds (+20%, P = 0.008) and lignin (+21%, P = 0.002) in roots, but not in (uninfected) stems or leaves (Figure 8 ). Neither PA treatment nor M. incognita infection alone affected these parameters.
Together with our metabolome data, these results indicate that PA initially reprograms PPP and flavonoid metabolism without significantly increasing the total abundance of these compounds, while also priming plants for local phenolic compound accumulation upon pathogen attack.