Similarly to pathogens, the interaction with beneficial microorganisms (such as growth–promoting rhizobacteria (PGPR) and Trichoderma) can induce in plants a form of immunity and is known as Induced Systemic Resistance (ISR), which renders plants resistant to subsequent attack by a broad spectrum of pathogens. Multidisciplinary strategies and high throughput global methodologies are contributing to understanding of the mechanisms underlying the ISR signaling network. It was demonstrated that diverse hormones play pivotal roles in the regulation of this network. From research executed with the genetic model plant Arabidopsis is has become apparent that the signalling pathways controlled by phytohormones cross-communicate, providing the plant with a powerful capacity to finely regulate its immune response. However, while the vast majority of the advances in the understanding of the plant immune signaling network has been carried out using Arabidopsis, relatively little information on plant immunity regulation in crop plants is known. This proposal aims to apply the Arabidopsis-derived molecular knowledge to the economically and ecologically important crop species tomato to: (1) elucidate the genetic control of resistance induced by beneficial soil-borne microorganisms (PGPR and Trichoderma) through a multidisciplinary approach and (2) identify similarities and differences between the immune signaling networks of these two different plant species. Using a combination of studies based on molecular biology, biochemistry, genomics and bioinformatics (analyses of gene expression by real-time PCR and microarrays, hormonal profiling, generation of transgenic plants using RNAi, among others) an integrative analysis of the mechanisms controlling ISR is proposed. The relevance of this proposal relies on its multidisciplinary aspects to address a fundamental question of plant induced defence, which will render critical information to apply fundamental science to crop improvement