Final Report Summary - TO THE ROOTS OF ISR (To the roots of induced systemic resistance in the Arabidopsis-Trichoderma-Fusarium tripartite interaction)
The central research objective of this project is to identify the plant responses originating in the roots that drive the ISR process in the Arabidopsis-Fusarium-Trichoderma interaction. This is achieved by a comparative genomics study of the tripartite interaction in Arabidopsis roots, with Fusarium oxysporum as soil-borne plant pathogen (expertise of outgoing host CSIRO Agriculture Brisbane, Australia) and Trichoderma spp. as BCO (expertise of return host CPMG, KU Leuven, Belgium). The unique characteristic of this project is to bridge research domains on Trichoderma and Fusarium plant responses, thereby focusing on the largely unknown processes that take place in plant roots.
In the project, the fellow has screened several Trichoderma strains belonging to different species for their biocontrol capacity through ISR. Highly promising biocontrol traits were discovered for a strain that had been isolated locally from a disease-suppressive soil. The strain, further termed Tg5, belongs to a species that is not yet well-known for its biocontrol capacities, but the fellow found that Tg5 is highly antimicrobial against a wide spectrum of pathogens and a good ISR-inducer as well. Interestingly, the fellow could also demonstrate that the metabolites secreted by the Tg5 strain are equally able to induce ISR in Arabidopsis against the soil-borne pathogen Fusarium oxysporum. Using a specially developed split-root assay, the fellow investigated the local and systemic ISR responses of Trichoderma-colonized Arabidopsis roots to the soil-borne pathogen Fusarium oxysporum at the transcriptome level. Moreover, the genome of the Tg5 strain was sequenced and a metabolic analysis identified the bioactive fraction in the Tg5 secretions. The analysis of the transcriptomic data showed the involvement of a large number of differentially expressed genes in Arabidopsis roots, that can be grouped in several significantly altered biological pathways. These included amongst others the modulation of hormonal biosynthesis and signaling as well as the induction of phenylpropanoid compounds. An interesting overlap was visible in the plant root responses to the Trichoderma strain, or to its metabolites alone. In addition, the beneficial Tg5 strain and the pathogenic F. oxysporum appeared to induce several similar patterns in the plant roots as well. In addition, the ISR-effect of the Tg5 strain as well as its metabolites was confirmed against the grey mould pathogen Botrytis cinerea in tomato.
The results of the project give a detailed insight into the root transcriptome response during the three-party interaction, and indicate that the Trichoderma strain, together with its bioactive metabolites, has very promising characteristics for use in practice. Moreover, the increased insight resulting from this project into how plant roots respond to such a beneficial fungus can help us to find more microbial candidates for biological control applications. In these ways this research project can contribute to the formation of integrated solutions for more sustainable pest management in our modern-day agriculture.