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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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Phenotypes of the Δste12 and Δtmk1 mutants compared to the parental strain (WT) and the complemented strain ste12-C2 upon growth on potato dextrose agar (PDA).(A) Hyphae of Δste12 and Δtmk1 mutants attached and formed hyphal aggregates in the colony periphery whereas the parental and the complemented strain showed hyphal avoidance. (B) Light microscopy of hyphae of the Δste12 and Δtmk1 mutants, the parental strain, and the complemented strain ste12-C2 upon growth on PDA with plain nylon fibers (approximate diameter 14 µm). Attachment to and growth along the fibers of hyphae of Δste12 and Δtmk1 mutants is marked with arrows.
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pone-0111636-g004: Phenotypes of the Δste12 and Δtmk1 mutants compared to the parental strain (WT) and the complemented strain ste12-C2 upon growth on potato dextrose agar (PDA).(A) Hyphae of Δste12 and Δtmk1 mutants attached and formed hyphal aggregates in the colony periphery whereas the parental and the complemented strain showed hyphal avoidance. (B) Light microscopy of hyphae of the Δste12 and Δtmk1 mutants, the parental strain, and the complemented strain ste12-C2 upon growth on PDA with plain nylon fibers (approximate diameter 14 µm). Attachment to and growth along the fibers of hyphae of Δste12 and Δtmk1 mutants is marked with arrows.

Mentions: During normal mycelial growth, hyphal tips are engaged in environmental sensing and usually avoid each other (negative autotropism) allowing the fungus to explore and exploit the available substrate whereas sub-apical hyphal parts generate new branches (reviewed in [42]). Microscopic analyses of Δste12 mycelia from the colony periphery revealed long hyphae with only few branches which aberrantly clustered by growing alongside each other thereby resulting in compact hyphal bundles (Fig. 4 A). This loss of hyphal avoidance was also apparent in Δtmk1 mutants but not in the parental strain and the complemented strain ste12-C2 which at the colony periphery formed typical branched hyphae that grew away from their neighbours.


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)

Phenotypes of the Δste12 and Δtmk1 mutants compared to the parental strain (WT) and the complemented strain ste12-C2 upon growth on potato dextrose agar (PDA).(A) Hyphae of Δste12 and Δtmk1 mutants attached and formed hyphal aggregates in the colony periphery whereas the parental and the complemented strain showed hyphal avoidance. (B) Light microscopy of hyphae of the Δste12 and Δtmk1 mutants, the parental strain, and the complemented strain ste12-C2 upon growth on PDA with plain nylon fibers (approximate diameter 14 µm). Attachment to and growth along the fibers of hyphae of Δste12 and Δtmk1 mutants is marked with arrows.
© Copyright Policy
Related In: Results  -  Collection

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

pone-0111636-g004: Phenotypes of the Δste12 and Δtmk1 mutants compared to the parental strain (WT) and the complemented strain ste12-C2 upon growth on potato dextrose agar (PDA).(A) Hyphae of Δste12 and Δtmk1 mutants attached and formed hyphal aggregates in the colony periphery whereas the parental and the complemented strain showed hyphal avoidance. (B) Light microscopy of hyphae of the Δste12 and Δtmk1 mutants, the parental strain, and the complemented strain ste12-C2 upon growth on PDA with plain nylon fibers (approximate diameter 14 µm). Attachment to and growth along the fibers of hyphae of Δste12 and Δtmk1 mutants is marked with arrows.
Mentions: During normal mycelial growth, hyphal tips are engaged in environmental sensing and usually avoid each other (negative autotropism) allowing the fungus to explore and exploit the available substrate whereas sub-apical hyphal parts generate new branches (reviewed in [42]). Microscopic analyses of Δste12 mycelia from the colony periphery revealed long hyphae with only few branches which aberrantly clustered by growing alongside each other thereby resulting in compact hyphal bundles (Fig. 4 A). This loss of hyphal avoidance was also apparent in Δtmk1 mutants but not in the parental strain and the complemented strain ste12-C2 which at the colony periphery formed typical branched hyphae that grew away from their neighbours.

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