Dubraska Moreno-Ruiz,1 Linda Salzmann,1 Mark D. Fricker,2 Susanne Zeilinger,1 and Alexander Lichius1,*
1Department of Microbiology, University of Innsbruck, 6020 Innsbruck, Austria; [email protected] (D.M.-R.); [email protected] (L.S.); [email protected] (S.Z.)
2Department of Plant Sciences, University of Oxford, Oxford OX1 3RB, UK; [email protected]
Trichoderma atroviride is a mycoparasitic fungus used as biological control agent against fungal plant pathogens. The recognition and appropriate morphogenetic responses to prey-derived signals are essential for successful mycoparasitism. We established microcolony confrontation assays using T. atroviride strains expressing cell division cycle 42 (Cdc42) and Ras-related C3 botulinum toxin substrate 1 (Rac1) interactive binding (CRIB) reporters to analyse morphogenetic changes and the dynamic displacement of localized GTPase activity during polarized tip growth. Microscopic analyses showed that Trichoderma experiences significant polarity stress when approaching its fungal preys. The perception of prey-derived signals is integrated via the guanosine triphosphatase (GTPase) and mitogen-activated protein kinase (MAPK) signalling network, and deletion of the MAP kinases Trichoderma MAPK 1 (Tmk1) and Tmk3 affected T. atroviride tip polarization, chemotropic growth, and contact-induced morphogenesis so severely that the establishment of mycoparasitism was highly inefficient to impossible. The responses varied depending on the prey species and the interaction stage, reflecting the high selectivity of the signalling process. Our data suggest that Tmk3 affects the polarity-stress adaptation process especially during the pre-contact phase, whereas Tmk1 regulates contact-induced morphogenesis at the early-contact phase. Neither Tmk1 nor Tmk3 loss-of-function could be fully compensated within the GTPase/MAPK signalling network underscoring the crucial importance of a sensitive polarized tip growth apparatus for successful mycoparasitism.
Then, 490 nm LED light from a CoolLED p4000 LED unit was used at 5% of the full intensity to excite CRIB-GFP reporter molecules, and emission light between 515–545 nm was collected through a Nikon F66-413 quadband filter cube.
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J. Fungi (Basel)
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