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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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Colony morphology of Δste12 (B) in comparison to the parental strain (A) and the complemented strains ste12-C1(C) and ste12-C2(D) upon growth on potato dextrose agar at 28°C for up to 7 days.
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pone-0111636-g002: Colony morphology of Δste12 (B) in comparison to the parental strain (A) and the complemented strains ste12-C1(C) and ste12-C2(D) upon growth on potato dextrose agar at 28°C for up to 7 days.

Mentions: For functional characterization of T. atroviride ste12, we transformed the linearized ste12 deletion vector into T. atroviride protoplasts. Although all of the resulting 20 transformants showed hygroymcin B-resistance, PCR- and Southern blot-based screening resulted in only one mutant with homologous integration and deletion of the ste12 gene in a mitotically stable manner (Figure S1). Complemented strains were generated by introducing a 5141-kb fragment bearing the ste12 gene and its 5′ and 3′ regulatory regions into the Δste12 mutant. Two complemented transformants with an ectopically (ste12-C1) and homologously (ste12-C2) integrated ste12 gene, respectively, were selected and included in a subset of experiments. The Δste12 and complemented mutants exhibited growth rates similar to the parental strain on solid complete medium (PDA). However, deletion of ste12 resulted in somewhat altered colony development with a reduced production of aerial hyphae in the colony centre and a delayed concentrical conidial ring formation. Whereas in the parental and both complemented strains the onset of conidiation starts in the middle of the colony, conidial maturation started from the subperipheral zone in Δste12 (Fig. 2). Similar to the parental strain, conidiation in the Δste12 mutant was light-dependent and the number of conidia produced by Δste12 was similar to the parental strain (1.9±0.3 * 109 and 1.2±0.2 * 109, respectively).


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)

Colony morphology of Δste12 (B) in comparison to the parental strain (A) and the complemented strains ste12-C1(C) and ste12-C2(D) upon growth on potato dextrose agar at 28°C for up to 7 days.
© Copyright Policy
Related In: Results  -  Collection

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

pone-0111636-g002: Colony morphology of Δste12 (B) in comparison to the parental strain (A) and the complemented strains ste12-C1(C) and ste12-C2(D) upon growth on potato dextrose agar at 28°C for up to 7 days.
Mentions: For functional characterization of T. atroviride ste12, we transformed the linearized ste12 deletion vector into T. atroviride protoplasts. Although all of the resulting 20 transformants showed hygroymcin B-resistance, PCR- and Southern blot-based screening resulted in only one mutant with homologous integration and deletion of the ste12 gene in a mitotically stable manner (Figure S1). Complemented strains were generated by introducing a 5141-kb fragment bearing the ste12 gene and its 5′ and 3′ regulatory regions into the Δste12 mutant. Two complemented transformants with an ectopically (ste12-C1) and homologously (ste12-C2) integrated ste12 gene, respectively, were selected and included in a subset of experiments. The Δste12 and complemented mutants exhibited growth rates similar to the parental strain on solid complete medium (PDA). However, deletion of ste12 resulted in somewhat altered colony development with a reduced production of aerial hyphae in the colony centre and a delayed concentrical conidial ring formation. Whereas in the parental and both complemented strains the onset of conidiation starts in the middle of the colony, conidial maturation started from the subperipheral zone in Δste12 (Fig. 2). Similar to the parental strain, conidiation in the Δste12 mutant was light-dependent and the number of conidia produced by Δste12 was similar to the parental strain (1.9±0.3 * 109 and 1.2±0.2 * 109, respectively).

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