Hsp genes are differentially expressed during Trichoderma asperellum self-recognition, mycoparasitism and thermal stress.

Heat shock proteins (Hsp) are important factors in the response of organisms to oscillations in environmental conditions. Although Hsp have been studied for a long time, little is known about this protein class in Trichoderma species. Here we studied the expression of Hsp genes during T. asperellum growth, and mycoparasitism against two phytopathogens: Sclerotinia sclerotiorum and Fusarium oxysporum, as well as during thermal stress. The expression levels of these genes were observed by real-time PCR and they showed to be differentially expressed under these conditions. We verified that the TaHsp26c, TaHsp70b and TaHsp70c genes were differentially expressed over time, indicating that these genes can be developmentally regulated in T. asperellum. Except for TaHsp26a, all other genes analyzed were induced in the post-contact condition when T. asperellum was cultured in a confrontation plate assay against itself. Additionally, TaHsp26b, TaHsp26c, TaHsp90, TaHsp104a and TaHsp104b were induced during initial contact between T. asperellum hyphae, suggesting that these proteins must play a role in the organism´s self-recognition mechanism. When we examined gene expression during mycoparasitism, we observed that some genes were induced both by S. sclerotiorum and F. oxysporum, while others were not induced during interaction with either of the phytopathogens. Furthermore, we observed some genes induced only during confrontation against S. sclerotiorum, indicating that the expression of Hsp genes during mycoparasitism seems to be modulated by the phytopathogen. To assess whether such genes are expressed during temperature oscillations, we analyzed their transcription levels during thermal and cold shock. We observed that except for the TaHsp70c gene, all others presented high transcript levels when T. asperellum was submitted to high temperature (38 °C), indicating their importance in the response to heat stress. The TaHsp70c gene was significantly induced only in cold shock at 4 °C. Our results show the importance of Hsp proteins during self-recognition, mycoparasitism and thermal stress in T. asperellum.