Shoresh, M., Department of Biological Chemistry, Weizmann Institute of Science, Rehovot 76100, Israel
Yedidia, I., Department of Biological Chemistry, Weizmann Institute of Science, Rehovot 76100, Israel
Chet, I., Department of Biological Chemistry, Weizmann Institute of Science, Rehovot 76100, Israel

Trichoderma spp. are effective biocontrol agents for a number of soilborne plant pathogens, and some are also known for their ability to enhance plant growth. It was recently suggested that Trichoderma also affects induced systemic resistance (ISR) mechanism in plants. Analysis of signal molecules involved in defense mechanisms and application of specific inhibitors indicated the involvement of jasmonic acid and ethylene in the protective effect conferred by Trichoderma spp. against the leaf pathogen Pseudomonas syringae pv. lachrymans. Moreover, examination of local and systemic gene expression by real-time reverse transcription-polymerase chain reaction analysis revealed thai T. asperellum (T203) modulates the expression of genes involved in the jasmonate/ ethylene signaling pathways of ISR (Lox1, Pal1, ETR1, and CTR1) in cucumber plants. We further showed that a subsequent challenge of Trichoderma-preinoculated plants with the leaf pathogen P. syringae pv. lachrymans resulted in higher systemic expression of the pathogenesis-related genes encoding for chitinase 1, β-1,3-glucanase, and peroxidase relative to noninoculated, challenged plants. This indicates that Trichoderma induced a potentiated state in the plant enabling it to be more resistant to subsequent pathogen infection.