A Trichoderma atroviride stress‐activated MAPK pathway integrates stress and light signals

Abstract

Cells possess stress-activated protein kinase (SAPK) signalling pathways, which are activated practically in response to any cellular insult, regulating responses for survival and adaptation to harmful environmental changes. To understand the function of SAPK pathways in T. atroviride, mutants lacking the MAPKK Pbs2 and the MAPK Tmk3 were analysed under several cellular stresses, and in their response to light. All mutants were highly sensitive to cellular insults such as osmotic and oxidative stress, cell wall damage, high temperature, cadmium, and UV irradiation. Under oxidative stress, the Tmk3 pathway showed specific roles during development, which in conidia are essential for tolerance to oxidant agents and appear to play a minor role in mycelia. The function of this pathway was more evident in Δpbs2 and Δtmk3 mutant strains when combining oxidative stress or cell wall damage with light. Light stimulates tolerance to osmotic stress through Tmk3 independently of the photoreceptor Blr1. Strikingly, photoconidiation and expression of blue light regulated genes was severally affected in Δtmk3 and Δpbs2 strains, indicating that this pathway regulates light responses. Furthermore, Tmk3 was rapidly phosphorylated upon light exposure. Thus, our data indicate that Tmk3 signalling cooperates with the Blr photoreceptor complex in the activation of gene expression.

Histone Deacetylase HDA-2 Regulates Trichoderma atroviride Growth, Conidiation, Blue Light Perception, and Oxidative Stress Responses

“…In this regard, similar results for light-regulated genes were published for T. atroviride and Aspergillus nidulans mutants in the tmk3 and sakA genes that code for a mitogen-activated protein kinase (MAPK) orthologous to Hog1p of S. cerevisiae. Importantly, Tmk3 and SakA integrate several stress factors, such as light sensing, stress sensing, and osmosensing (35,36). It is worth noting that in yeast under hyperosmotic stress the repressor Sko1 is phosphorylated by Hog1 and converted to an activator that recruits Hog1 itself as well as the SAGA histone acetyltransferase complex (coactivator) at the promoter of target genes to activate transcription (37).…”

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

“…Blue light, for example, leads to the suppression of conidiation and enhanced virulence in Botrytis cinerea [ 15 ], while it induces conidiation in species of Trichoderma [ 16 , 17 ]. In T. atroviride , the stress-activated MAP kinase Tmk3 undergoes rapid phosphorylation when the fungus is exposed to light, and signaling via Tmk3 was reported to act in concert with the Blr photoreceptor complex (WCC homologue; consisting of Blr-1 and Blr-2) in the activation of expression of genes regulated by blue light [ 18 ].…”

“…Tmk3 (Hog1) is part of the conserved stress-activated protein kinase (SAPK) signaling cascade that governs pathogenicity, asexual reproduction, and circadian rhythms in response to osmotic-, oxidative-, heavy metal-, and injury-caused stress in various fungi [ 6 , 33 , 34 , 35 , 36 , 37 , 38 , 39 , 40 , 41 ]. Light is another environmental cue that triggers the SAPK pathway [ 18 , 41 , 42 ]. In T. atroviride IMI206040, Tmk3 phosphorylation is connected to Blr-1-dependent blue light sensing [ 18 ], and in A. nidulans , initiation of the pathway by red light has been reported [ 42 ].…”

“…Light is another environmental cue that triggers the SAPK pathway [ 18 , 41 , 42 ]. In T. atroviride IMI206040, Tmk3 phosphorylation is connected to Blr-1-dependent blue light sensing [ 18 ], and in A. nidulans , initiation of the pathway by red light has been reported [ 42 ].…”

Two hybrid histidine kinases, TcsB and the phytochrome FphA, are involved in temperature sensing in Aspergillus nidulans

“…Small temperature increases in the morning indicate the upcoming, “stressful” day. Such an alerting function has been proposed for light, and it was shown that the light responses in A. nidulans , A. alternata and Trichoderma atroviride share the central stress pathway, the HOG pathway, or are linked to it (Fuller et al , ; Esquivel‐Naranjo et al , ; Fischer et al , ; Yu et al , ; Igbalajobi et al , ; Yu and Fischer, ). Temperature sensing hence allows stress adaptations underground in the dark.…”