Native soils with their microbiotas elicit a state of alert in tomato plants

Several studies have investigated soil microbial biodiversity, but understanding of the mechanisms underlying plant responses to soil microbiota remains in its infancy. Here, we focused on tomato (Solanum lycopersicum), testing the hypothesis that plants grown on native soils display different responses to soil microbiotas. Using transcriptomics, proteomics, and biochemistry, we describe the responses of two tomato genotypes (susceptible or resistant to Fusarium oxysporum f. sp. lycopersici) grown on an artificial growth substrate and two native soils (conducive and suppressive to Fusarium). Native soils affected tomato responses by modulating pathways involved in responses to oxidative stress, phenol biosynthesis, lignin deposition, and innate immunity, particularly in the suppressive soil. In tomato plants grown on steam-disinfected soils, total phenols and lignin decreased significantly. The inoculation of a mycorrhizal fungus partly rescued this response locally and systemically. Plants inoculated with the fungal pathogen showed reduced disease symptoms in the resistant genotype in both soils, but the susceptible genotype was partially protected from the pathogen only when grown on the suppressive soil. The 'state of alert' detected in tomatoes reveals novel mechanisms operating in plants in native soils and the soil microbiota appears to be one of the drivers of these plant responses.

Not only priming: Soil microbiota may protect tomato from root pathogens

An increasing number of studies have investigated soil microbial biodiversity. However, the mechanisms regulating plant responses to soil microbiota are largely unknown. A previous work tested the hypothesis that tomato plants grown on native soils with their complex microbiotas respond differently from tomato growing in a sterile substrate. Two soils, suppressive or conducive to Fusarium oxysporum f. sp. lycopersici (FOL), and two genotypes susceptible and resistant to the same pathogen were considered. The work highlighted that the two tested soil microbiotas, irrespectively of their taxonomic composition, elicit the PAMP-triggered Immunity Pathway, the first level of plant defence, as well as an increased lignin synthesis, leading to an active protection when FOL is present in the soil. Here, we tested the expression of a panel of genes involved in Effector-Triggered Immunity (ETI), demonstrating that soil microbiota, beside genotype, affects plant resistance to FOL also modulating this pathway.