Phyto-Friendly Soil Bacteria and Fungi Provide Beneficial Outcomes in the Host Plant by Differently Modulating Its Responses through (In)Direct Mechanisms

Sustainable agricultural systems based on the application of phyto-friendly bacteria andfungi are increasingly needed to preserve soil fertility and microbial biodiversity, as well as to reducethe use of chemical fertilizers and pesticides. Although there is considerable attention on the potentialapplications of microbial consortia as biofertilizers and biocontrol agents for crop management,knowledge on the molecular responses modulated in host plants because of these beneficial associationsis still incomplete. This review provides an up-to-date overview of the different mechanisms ofaction triggered by plant-growth-promoting microorganisms (PGPMs) to promote host-plant growthand improve its defense system. In addition, we combined available gene-expression profiling datafrom tomato roots sampled in the early stages of interaction with Pseudomonas or Trichoderma strainsto develop an integrated model that describes the common processes activated by both PGPMs andhighlights the host's different responses to the two microorganisms. All the information gatheredwill help define new strategies for the selection of crop varieties with a better ability to benefit fromthe elicitation of microbial inoculants.