Suppression subtractive hybridization analysis provides new insights into the tomato (Solanum lycopersicum L.) response to the plant probiotic microorganism Trichoderma longibrachiatum MK1 created by Monica De Palma, Nunzio D’Agostino, Silvia Proietti, Laura Bertini, Matteo Lorito, Michelina Ruocco, Carla Caruso, Maria L. Chiusano and Marina Tucci

Trichoderma species include widespread rhizosphere-colonising fungi that may establish an opportunistic interaction with the plant, resulting in growth promotion and/or increased tolerance to biotic and abiotic stresses. For this reason, Trichoderma-based formulations are largely used in agriculture to improve yield while reducing the application of agro-chemicals. By using the Suppression Subtractive Hybridization method, we identified molecular mechanisms activated during the in vitro interaction between tomato (Solanum lycopersicum L.) and the selected strain MK1 of Trichoderma longibrachiatum, and which may participate in the stimulation of plant growth and systemic resistance. Screening and sequence analysis of the subtractive library resulted in forty unique transcripts. Their annotation in functional categories revealed enrichment in cell defence/stress and primary metabolism categories, while secondary metabolism and transport were less represented. Increased transcription of genes involved in defence, cell wall reinforcement and signalling of reactive oxygen species suggests that improved plant pathogen resistance induced by T. longibrachiatum MK1 in tomato may occur through stimulation of the above mechanisms. The array of activated defence-related genes indicates that different signalling pathways, beside the jasmonate/ethylene-dependent one, collaborate to fine-tune the plant response. Our results also suggest that the growth stimulation effect of MK1 on tomato may involve a set of genes controlling protein synthesis and turnover as well as energy metabolism and photosynthesis. Transcriptional profiling of several defence-related genes at different time points of the tomato–Trichoderma interaction, and after subsequent inoculation with the pathogen Botrytis cinerea, provided novel information on genes that may specifically modulate the tomato response to T. longibrachiatum, B. cinerea or both.