Transcriptome and Metabolome Reprogramming in Tomato Plants by T22 Primes and Enhances Defense Responses Against Aphids.

Beneficial fungi in the genus are among the most widespread biocontrol agents of plant pathogens. Their role in triggering plant defenses against pathogens has been intensely investigated, while, in contrast, very limited information is available on induced barriers active against insects. The growing experimental evidence on this latter topic looks promising, and paves the way toward the development of strains and/or consortia active against multiple targets. However, the predictability and reproducibility of the effects that these beneficial fungi is still somewhat limited by the lack of an in-depth understanding of the molecular mechanisms underlying the specificity of their interaction with different crop varieties, and on how the environmental factors modulate this interaction. To fill this research gap, here we studied the transcriptome changes in tomato plants (cultivar "Dwarf San Marzano") induced by (strain T22) colonization and subsequent infestation by the aphid . A wide transcriptome reprogramming, related to metabolic processes, regulation of gene expression and defense responses, was induced both by separate experimental treatments, which showed a synergistic interaction when concurrently applied. The most evident expression changes of defense genes were associated with the multitrophic interaction -tomato-aphid. Early and late genes involved in direct defense against insects were induced (i.e., ), along with indirect defense genes, such as and . Targeted and untargeted semi-polar metabolome analysis revealed a wide metabolome alteration showing an increased accumulation of isoprenoids in treated plants. The wide array of transcriptomic and metabolomics changes nicely fit with the higher mortality of aphids when feeding on treated plants, herein reported, and with the previously observed attractiveness of these latter toward the aphid parasitoid . Moreover, treated plants showed the over-expression of transcripts coding for several families of defense-related transcription factors (bZIP, MYB, NAC, AP2-ERF, WRKY), suggesting that the fungus contributes to the priming of plant responses against pest insects. Collectively, our data indicate that treatment of tomato plants induces transcriptomic and metabolomic changes, which underpin both direct and indirect defense responses.