Influence of Different Light Regimes on the Mycoparasitic Activity and 6-Pentyl-α-pyrone Biosynthesis in Two Strains of Trichoderma atroviride

Abstract

The ascomycete Trichoderma atroviride is well known for its mycoparasitic lifestyle. Similar to other organisms, light is an important cue for T. atroviride. However, besides triggering of conidiation, little is known on the physiological responses of T. atroviride to light. In this study, we analyzed how cultivation under different light wavelengths and regimes impacted the behavior of two T. atroviride wild-type strains: IMI206040 and P1. While colony extension of both strains was slightly affected by light, massive differences in their photoconidation responses became evident. T. atroviride P1 colonies conidiated under all conditions tested including growth in complete darkness, while IMI206040 required white, blue or green light to trigger asexual reproduction. Interestingly, deletion of the stress-activated MAP kinase-encoding gene tmk3 abolished the ability of strain P1 to conidiate in red and yellow light as well as in darkness. Furthermore, light-dependent differences in the mycoparasitic activity and in the biosynthesis of the secondary metabolite 6-pentyl-α-pyrone (6-PP) became evident. 6-PP production was highest upon dark incubation, while light, especially exposure to white light as light/dark cycles, had an inhibitory effect on its biosynthesis. We conclude that the response of T. atroviride to light is strain-dependent and impacts differentiation, mycoparasitism, and 6-PP production; hence, this should be considered in experiments testing the mycoparasitic activity of these fungi.

Stress-Activated Protein Kinase Signalling Regulates Mycoparasitic Hyphal-Hyphal Interactions in Trichoderma atroviride

“…The outcome of mycoparasitic interactions, of course, also depends on additional conditions. For instance, we recently showed that the ability of T. atroviride to mycoparasitise F. oxysporum is light regulated and successful under yellow or red light as well as in complete darkness [ 42 ]. One possible explanation for this phenomenon is that the light-dependent mycotoxin production of F. oxysporum [ 61 ] is so significantly reduced that T. atroviride can overcome its defence response.…”

“…Our previous studies showed that deletion of tmk1 and tmk3 significantly reduced the mycoparasitic abilities of T. atroviride in comparison to the wild-type strain [ 32 , 42 ]. By analogy to the role of the F. oxysporum homologue, Fusarium MAPK 1 (Fmk1), in plant sensing [ 77 ], Tmk1 is suspected to be governed by pheromone receptors to sense prey-derived signals.…”

“…The cellular basis for the reduced virulence in the mutant strains thus remained largely unexplained. For the recently generated ∆ tmk3 mutant [ 42 ], this is the first study to investigate the cellular basis of its avirulence. Our analyses suggest that the reduction in mycoparasitic virulence of ∆ tmk3 and ∆ tmk1 are quantitative effects, resulting from the reduced abilities to restore polarised tip growth upon prey-induced depolarisation, and to establish contact to prey hyphae, respectively.…”

“…Quantitative CRIB analyses revealed that focused GTPase activity clusters can no longer be established, but are instead randomly dispersed along the cell apex leading to the characteristic corrupted phenotype known from typical cell polarity mutants [ 30 , 88 , 89 , 90 , 91 ]. The induced polarity defect makes it impossible for the mutant to establish functional mycoparasitic contacts and renders it avirulent as previously noted [ 42 ]. A direct link between stress signalling via the Hog1-ortholog SAPK suppressor of tyrosine phosphatase (Sty1) and Cdc42-dependent cell polarity has recently been established in fission yeast using CRIB reporters [ 92 ].…”

“…Trichoderma atroviride (strain P1; ATCC 74058), Δ tmk1 [ 32 ], and Δ tmk3 [ 42 ] were used as mycoparasites. The plant pathogens Botrytis cinerea B05.10, B. cinerea B05.10 dsRed strain [ 43 ], Fusarium oxysporum f. sp.…”