Development of a screening system for ISR-inducing Trichoderma spp. based on ISR-marker genes

Abstract: Since classical disease assays are labour‐ and time‐consuming, and even more so in tripartite interactions, the discovery of general markers for induced systemic resistance (ISR) can greatly facilitate the search for novel or more efficient biocontrol organisms. We have reported that application of Trichoderma hamatum T382 to Arabidopsis thaliana roots resulted in ISR against leaf infection by the necrotrophic pathogen Botrytis cinerea and performed a genome-wide analysis of ISR-related leaf gene expression, both before and after B. cinerea infection. In addition, we recently completed a similar microarray analysis with tomato replacing A. thaliana in the tripartite interaction. Based on the comparison of the transcriptomic analyses in both plants, a series of orthologous genes up-regulated in both tripartite systems was selected. In a next step, we evaluated which of these genes could be considered as general markers for Trichoderma-induced ISR. Our analysis revealed 4 promising ISR marker genes, which we used to develop a screening system for fast and effective visual detection of ISR-inducing Trichoderma spp., based on pMarker-GUS lines in A. thaliana. The potential of the pMarker-GUS lines as a screening tool for identification of ISR-inducing Trichoderma strains was demonstrated by the clear correlation between the percentage of disease reduction and the degree of staining of the pMarker-GUS lines. Most importantly, the ISR-inducing Trichoderma strains identified by the pMarker-GUS lines in A. thaliana also showed ISR against B. cinerea in tomato, thus proving the validity of our screening approach.