PROTEIN HYTRA1 SECRETED BY TRICHODERMA PLAYS A KEY ROLE IN INDUCED SYSTEMIC RESISTANCE.

Trichoderma harzianum T22 is one of the Trichoderma isolatesmost used as active ingredient in commercial bio-fungicides andbio-fertilizers. In addition to their mycoparasitic abilities, manyTrichoderma strains can colonize and grow in association withplant roots and can significantly increase plant growth, developmentand systemic resistance to pathogen attack. During Trichoderma–plant interaction, a plant response has been confirmed asresponsible for at least part of the protection effect, but the molecularmechanisms involved are still largely unknown. The proteinHytra1 secreted by Trichoderma was tested for its ability toinduce a hypersensitive reaction (HR) and induced systemic resistancein tomato plants. Hytra1 infiltration elicited a strong HRon tomato leaves and could trigger plant defence reactions subsequentto pathogen infections both locally and systemically. Physiologicalanalyses of tomato leaves treated with Hytra1 showedthat this hydrophobin can induce an oxidative burst in plantcells. Low Hytra1 concentrations also triggered activation of theantioxidant system that controls accumulation of reactive oxygenspecies (superoxide anions and peroxides). This modulationplays a role in transduction of the oxidative signal, leading to formationof signal molecules (lipoperoxides) that trigger the accumulationof defence molecules (e.g. riscitin) and PR proteins. Real-time PCR analysis of RNA extracted from tomato plants 24hours after treatment with 0.31 μM Hytra1 showed strong activationof PR4 transcription, while PR1 expression was induced to alesser extent in the same conditions. Steady-state mRNA levels ofPR4 and PR1 were about 13-fold and 5-fold higher, respectively,than in controls.