An integrated “omics” approach to unravel the impact of root symbionts on tomato direct and indirect defenses against insect herbivores

As sessile organisms, plants are constantly under attack by insect herbivores. To defend themselves, they have developed a broad array of direct and indirect defense mechanisms. Plants can also build mutualistic relationships with several microbes that are hosted in their rhizosphere. These microbes provide their hosts with essential services, such as improved mineral uptake, nitrogen fixation, growth promotion, and protection from pathogens and insect herbivores. Among these beneficial microbes, the arbuscular mycorrhizal fungus (AMF) Rhizophagus irregularis and the plant growth-promoting fungus (PGPF) Trichoderma harzianum have been broadly studied. In the present doctoral study, tomato (Solanum lycopersicum) was used as a model plant to investigate the effect of R. irregularis and T. harzianum on modulating tomato’s direct and indirect defenses against insect herbivores. Overall, the study aims to explore the potential of using beneficial root fungi in protecting crop plants against insect herbivores. In this frame, a series of experiments, comprising transcriptomic and metabolomic approaches, was conducted aiming to illuminate aspects of plant-microbe-insect interactions that are less studied and contribute to the transformation of conventional to sustainable Agriculture. Conclusively, the results presented in this doctoral thesis indicate that the beneficial root fungi R. irregularis and T. harzianum mediate plant-insect interactions and can trigger important effects over the three trophic levels: namely the plant, its herbivores, and their natural enemies. Therefore, these findings reinforce the potential of beneficial root fungi to be used in Agriculture as a promising alternative tool to reduce the use of chemical insecticides, ensure crop productivity and food security, and protect human health as well as the environment