Involvement of jasmonic acid, ethylene and salicylic acid signaling pathways behind the systemic resistance induced by Trichoderma longibrachiatum H9 in cucumber

Abstract Background Trichoderma spp. are effective biocontrol agents for many plant pathogens, thus the mechanism of Trichoderma-induced plant resistance is not fully understood. In this study, a novel Trichoderma strain was identified, which could promote plant growth and reduce the disease index of gray mold caused by Botrytis cinerea in cucumber. To assess the impact of Trichoderma inoculation on the plant response, a multi-omics approach was performed in the Trichoderma-inoculated cucumber plants through the analyses of the plant transcriptome, proteome, and phytohormone content. Results A novel Trichoderma strain was identified by morphological and molecular analysis, here named T. longibrachiatum H9. Inoculation of T. longibrachiatum H9 to cucumber roots promoted plant growth in terms of root length, plant height, and fresh weight. Root colonization of T. longibrachiatum H9 in the outer layer of epidermis significantly inhibited the foliar pathogen B. cinerea infection in cucumber. The plant transcriptome and proteome analyses indicated that a large number of differentially expressed genes (DEGs) and differentially expressed proteins (DEPs) were identified in cucumber plants 96 h post T. longibrachiatum H9 inoculation. Up-regulated DEGs and DEPs were mainly associated with defense/stress processes, secondary metabolism, and phytohormone synthesis and signaling, including jasmonic acid (JA), ethylene (ET) and salicylic acid (SA), in the T. longibrachiatum H9-inoculated cucumber plants in comparison to untreated plants. Moreover, the JA and SA contents significantly increased in cucumber plants with T. longibrachiatum H9 inoculation. Conclusions Application of T. longibrachiatum H9 to the roots of cucumber plants effectively promoted plant growth and significantly reduced the disease index of gray mold caused by B. cinerea. The analyses of the plant transcriptome, proteome and phytohormone content demonstrated that T. longibrachiatum H9 mediated plant systemic resistance to B. cinerea challenge through the activation of signaling pathways associated with the phytohormones JA/ET and SA in cucumber