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The transcription factor Ste12 mediates the regulatory role of the Tmk1 MAP kinase in mycoparasitism and vegetative hyphal fusion in the filamentous fungus Trichoderma atroviride.

Gruber S, Zeilinger S - PLoS ONE (2014)

Bottom Line: However, the transcription factors acting downstream of Tmk1 are hitherto unknown.Here we analyzed the functions of the T. atroviride Ste12 transcription factor whose orthologue in yeast is targeted by the Fus3 and Kss1 MAP kinases.Aerial hyphae formation and conidiation, in contrast, were found to be independent of Ste12.

View Article: PubMed Central - PubMed

Affiliation: Research Area Biotechnology and Microbiology, Institute of Chemical Engineering, Vienna University of Technology, Wien, Austria.

ABSTRACT
Mycoparasitic species of the fungal genus Trichoderma are potent antagonists able to combat plant pathogenic fungi by direct parasitism. An essential step in this mycoparasitic fungus-fungus interaction is the detection of the fungal host followed by activation of molecular weapons in the mycoparasite by host-derived signals. The Trichoderma atroviride MAP kinase Tmk1, a homolog of yeast Fus3/Kss1, plays an essential role in regulating the mycoparasitic host attack, aerial hyphae formation and conidiation. However, the transcription factors acting downstream of Tmk1 are hitherto unknown. Here we analyzed the functions of the T. atroviride Ste12 transcription factor whose orthologue in yeast is targeted by the Fus3 and Kss1 MAP kinases. Deletion of the ste12 gene in T. atroviride not only resulted in reduced mycoparasitic overgrowth and lysis of host fungi but also led to loss of hyphal avoidance in the colony periphery and a severe reduction in conidial anastomosis tube formation and vegetative hyphal fusion events. The transcription of several orthologues of Neurospora crassa hyphal fusion genes was reduced upon ste12 deletion; however, the Δste12 mutant showed enhanced expression of mycoparasitism-relevant chitinolytic and proteolytic enzymes and of the cell wall integrity MAP kinase Tmk2. Based on the comparative analyses of Δste12 and Δtmk1 mutants, an essential role of the Ste12 transcriptional regulator in mediating outcomes of the Tmk1 MAPK pathway such as regulation of the mycoparasitic activity, hyphal fusion and carbon source-dependent vegetative growth is suggested. Aerial hyphae formation and conidiation, in contrast, were found to be independent of Ste12.

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Model of the role of Ste12 as down-stream target of the Tmk1 MAP kinase pathway and as target of additional, still unknown pathways.
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pone-0111636-g009: Model of the role of Ste12 as down-stream target of the Tmk1 MAP kinase pathway and as target of additional, still unknown pathways.

Mentions: To substantiate a putative role of Ste12 in the mediation of mycoparasitism-relevant processes and as a functional target of the Tmk1 MAP kinase, the ste12 gene was deleted in T. atroviride. Comparative analyses of the phenotypes of Δste12 and Δtmk1 mutants revealed that several of the Tmk1 MAPK outputs are mediated by Ste12 (Fig. 9). The Δste12 and Δtmk1 mutants shared defects in hyphal avoidance and anastomosis and showed similar carbon-source utilization profiles and alterations in mycoparasitism-related processes, with the latter, however, being more pronounced upon tmk1 deletion. Also differences between Δste12 and Δtmk1 mutants were found which suggests that additional transcription factors other than Ste12 are targeted by Tmk1. As reported previously, Δtmk1 mutants form “flat” colonies with only few aerial hyphae, show reduced hyphal growth rates on PDA and sporulate light-independently [17], [23]. In the present study we further found that tmk1 deletion resulted in a delay in germ tube elongation, similar to what has been reported for N. crassa mak-2 deletion strains and which indicates that a functional MAPK is required for optimal apical hyphal extension [46]. In contrast, T. atroviride Ste12 is dispensable for hyphal extension and is not involved in mediating the repressing effect of Tmk1 on conidiation in the dark; furthermore, it plays only a minor role in aerial hyphae formation.


The transcription factor Ste12 mediates the regulatory role of the Tmk1 MAP kinase in mycoparasitism and vegetative hyphal fusion in the filamentous fungus Trichoderma atroviride.

Gruber S, Zeilinger S - PLoS ONE (2014)

Model of the role of Ste12 as down-stream target of the Tmk1 MAP kinase pathway and as target of additional, still unknown pathways.
© Copyright Policy
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4214791&req=5

pone-0111636-g009: Model of the role of Ste12 as down-stream target of the Tmk1 MAP kinase pathway and as target of additional, still unknown pathways.
Mentions: To substantiate a putative role of Ste12 in the mediation of mycoparasitism-relevant processes and as a functional target of the Tmk1 MAP kinase, the ste12 gene was deleted in T. atroviride. Comparative analyses of the phenotypes of Δste12 and Δtmk1 mutants revealed that several of the Tmk1 MAPK outputs are mediated by Ste12 (Fig. 9). The Δste12 and Δtmk1 mutants shared defects in hyphal avoidance and anastomosis and showed similar carbon-source utilization profiles and alterations in mycoparasitism-related processes, with the latter, however, being more pronounced upon tmk1 deletion. Also differences between Δste12 and Δtmk1 mutants were found which suggests that additional transcription factors other than Ste12 are targeted by Tmk1. As reported previously, Δtmk1 mutants form “flat” colonies with only few aerial hyphae, show reduced hyphal growth rates on PDA and sporulate light-independently [17], [23]. In the present study we further found that tmk1 deletion resulted in a delay in germ tube elongation, similar to what has been reported for N. crassa mak-2 deletion strains and which indicates that a functional MAPK is required for optimal apical hyphal extension [46]. In contrast, T. atroviride Ste12 is dispensable for hyphal extension and is not involved in mediating the repressing effect of Tmk1 on conidiation in the dark; furthermore, it plays only a minor role in aerial hyphae formation.

Bottom Line: However, the transcription factors acting downstream of Tmk1 are hitherto unknown.Here we analyzed the functions of the T. atroviride Ste12 transcription factor whose orthologue in yeast is targeted by the Fus3 and Kss1 MAP kinases.Aerial hyphae formation and conidiation, in contrast, were found to be independent of Ste12.

View Article: PubMed Central - PubMed

Affiliation: Research Area Biotechnology and Microbiology, Institute of Chemical Engineering, Vienna University of Technology, Wien, Austria.

ABSTRACT
Mycoparasitic species of the fungal genus Trichoderma are potent antagonists able to combat plant pathogenic fungi by direct parasitism. An essential step in this mycoparasitic fungus-fungus interaction is the detection of the fungal host followed by activation of molecular weapons in the mycoparasite by host-derived signals. The Trichoderma atroviride MAP kinase Tmk1, a homolog of yeast Fus3/Kss1, plays an essential role in regulating the mycoparasitic host attack, aerial hyphae formation and conidiation. However, the transcription factors acting downstream of Tmk1 are hitherto unknown. Here we analyzed the functions of the T. atroviride Ste12 transcription factor whose orthologue in yeast is targeted by the Fus3 and Kss1 MAP kinases. Deletion of the ste12 gene in T. atroviride not only resulted in reduced mycoparasitic overgrowth and lysis of host fungi but also led to loss of hyphal avoidance in the colony periphery and a severe reduction in conidial anastomosis tube formation and vegetative hyphal fusion events. The transcription of several orthologues of Neurospora crassa hyphal fusion genes was reduced upon ste12 deletion; however, the Δste12 mutant showed enhanced expression of mycoparasitism-relevant chitinolytic and proteolytic enzymes and of the cell wall integrity MAP kinase Tmk2. Based on the comparative analyses of Δste12 and Δtmk1 mutants, an essential role of the Ste12 transcriptional regulator in mediating outcomes of the Tmk1 MAPK pathway such as regulation of the mycoparasitic activity, hyphal fusion and carbon source-dependent vegetative growth is suggested. Aerial hyphae formation and conidiation, in contrast, were found to be independent of Ste12.

Show MeSH
Related in: MedlinePlus