InduResTom · Induced Resistance in tomato by beneficial microorganisms - Translating Arabidopsis-derived molecular knowledge on defense signaling

Induced Resistance in tomato by beneficial microorganisms - Translating Arabidopsis-derived molecular knowledge on defense signaling.

To combat invasion by pathogens, plants have evolved a sophisticated immune system that, like the animal innate immune system, recognizes attack by alien organisms, and responds by activating specific defenses directed against the invader. Beneficial soil-borne microorganisms, such as plant growth–promoting rhizobacteria and Trichoderma sp. can induce a phenotypically similar form of systemic immunity called Induced Systemic Resistance (ISR). ISR is effective against a broad spectrum of plant pathogens and provides an attractive tool for the development of durable and environmentally friendly strategies for crop protection. Accordingly, the potential for microbes to enhance crop production has garnered the attention of both large and small producers. However the vast majority of the advances in the understanding of the complexity of the plant immune signaling network that is recruited by beneficial and parasitic organisms have been carried out using the model plant Arabidopsis, while the information on crop plants is still very scarce. The main aim of InduResTom was to apply the Arabidopsis-derived molecular knowledge on plant immunity to the economically and ecologically important species tomato, to generate knowledge about the genetic control of the plant defense related processes underlying the interaction of this crop with beneficial microorganisms that induce resistance. By performing different bioassays and by using molecular techniques we found that similarly to ISR triggered by beneficial rhizobacteria in Arabidopsis shoots, Trichoderma-ISR is able to protect tomato plants against different leaf pathogens including bacterial pathogens, biotrophic oomycetes and necrotrophic fungi. Further, Trichoderma was also effective protecting plants against generalist herbivores, pointing to an enormous potential of the use of Trichoderma as a low-input way for crop protection. By using biochemical and molecular techniques, and tomato and Arabidopsis mutant lines we studied the main hormonal signaling components involved in the ISR phenomena against leaf pathogens, and we found that although several hormone-regulated signaling pathways are required for ISR elicited by Trichoderma, priming was detected in shoots only for jasmonic acid (JA)-regulated defense responses and callose-containing papillae that were induced by pathogen infection. These findings are in line with the majority of evidences supporting a central role of JA/Ethylene (Et) in induced resistance by beneficial associations in Arabidopsis shoots. Much less is known about what extend is this model valid for root protection. Belowground detrimental organisms include microbial pathogens, herbivores, arthropod and parasitic nematodes which have strong impact on plant fitness. In our project we observed that similarly to shoot tissues; Trichoderma is able to protect tomato roots against root knot nematodes both at local and systemic level, pointing again to a huge potential of this beneficial fungus as a biocontrol agent against different detrimental organisms. However induction of resistance in the root tissues involves additional hormonal signals different to the classical JA/Ethylene (Et)-regulated pathways. We found that root protection by Trichoderma against nematodes takes place at multiple stages of infection: invasion, root knot development and reproduction. According with the clear boundary of plant responses to nematode attack between the initial and later stages of infection, we found that the alteration of host responses triggered by Trichoderma is highly dependent on the stage of the nematode infection. We found that salycilic acid (SA)-mediated defenses that are activated in the plant in the first stages of infection were enhanced by Trichoderma, and protected plants against nematode invasion. At later stages of infection, the nematode actively suppresses JA-mediated plant defenses, but Trichoderma is able to diminish this suppression, affecting the nematode ability for feeding and reproduction. Finally, at the last stages of reproduction, the nematodes eggs trigger SA-mediated defenses, which were potentiated by Trichoderma. Our results showed for first time the phenotypic plasticity of the priming phenomena that is induced belowground against complex attackers. This novel concept of phenotypic plasticity of priming belowground can be used to optimize or develop novel strategies for crop protection. Beside the key role of the SA and JA hormonal pathways in the transduction of signaling during ISR, we found that they also regulate the direct interaction between Trichoderma and the plant root. By using confocal microscopy, molecular techniques and by using bioassays with hormonal impaired mutants and exogenous hormone application, we observed a main role for the SA related pathway (which plays key roles in plant defence against biotrophic pathogens) in plant control of Trichoderma endophytic root colonization. In our project we also found that besides root colonization, volatile organic compounds (VOCs) released by Trichoderma can induce systemic resistance in of Arabidopsis and tomato shoots. We characterized the specific genetic pathway activated by Trichoderma VOCs in tomato which leads to an enhanced plant defense. By using in vitro systems, bioassays, confocal microscopy and molecular and biochemical techniques we found that Trichoderma VOCs triggered in plant roots the iron deficiency response, including the upregulation of the transcription factor MYB72, which was mainly accumulated in epidermal cells, and a higher accumulation of the important signaling molecule Nitric Oxide (NO). Our results show that Trichoderma VOCs are able to prime shoots for a stronger JA-responsive gene expression, which leads to an enhanced defense against necrotrophic fungi and pathogenic bacteria. By using grafting experiments we found that the VOCs perceived by the root system suffice to prime JA-mediated defenses in the shoots. Further by using a pharmacological approach and mutant lines in Arabidopsis and tomato we found that NO plays a double function in the observed phenomenon: in the correct perception of Trichoderma VOCs by the root system and in the transduction of the response from the root to the shoot. InduResTom has allowed uncovering key elements in the defence signalling pathways induced by the beneficial fungus Trichoderma in the economically important species tomato. The results derived from this project will contribute to the improvement of crop protection by exploiting natural beneficial microorganisms that are able to boost plant defenses.

Текст от CORDIS, на английски · Данни: CORDIS, © Европейски съюз