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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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Mycoparasitic activity of the Δste12 mutant against R. solani and B. cinerea as hosts.(A) Plate confrontation assays of the Δste12 mutant (second panel), the parental strain (upper panel) and the complemented strains ste12-C1 (third panel) and ste12-C2 (fourth panel) against host fungi. Pictures were taken 1, 2, 3, and 14 days (R. solani) and 7 and 14 days (B. cinerea) after inoculation of the two fungi on opposite sides of the plate. (B) Microscopic analyses of the confrontation zone between T. atroviride (right side) and R. solani (left side). The Δste12 mutant approaches the host as aggregated hyphae with only single hyphae attaching to Rhizoctonia. Attachments to host hyphae are marked by arrows. The scale bar represents 50 µm. (C) Attachment to and coiling around host hyphae. Despite the inability of the Δste12 mutant to fully overgrow and parasitize B. cinerea, the mutant shows the typical mycoparasitism-associated coiling response.
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pone-0111636-g005: Mycoparasitic activity of the Δste12 mutant against R. solani and B. cinerea as hosts.(A) Plate confrontation assays of the Δste12 mutant (second panel), the parental strain (upper panel) and the complemented strains ste12-C1 (third panel) and ste12-C2 (fourth panel) against host fungi. Pictures were taken 1, 2, 3, and 14 days (R. solani) and 7 and 14 days (B. cinerea) after inoculation of the two fungi on opposite sides of the plate. (B) Microscopic analyses of the confrontation zone between T. atroviride (right side) and R. solani (left side). The Δste12 mutant approaches the host as aggregated hyphae with only single hyphae attaching to Rhizoctonia. Attachments to host hyphae are marked by arrows. The scale bar represents 50 µm. (C) Attachment to and coiling around host hyphae. Despite the inability of the Δste12 mutant to fully overgrow and parasitize B. cinerea, the mutant shows the typical mycoparasitism-associated coiling response.

Mentions: In order to assess whether Tmk1 regulates the mycoparasitic activity of T. atroviride by employing the Ste12 transcription factor and whether the observed aberrant self-attachment of Δste12 impacts the mycoparasitic interaction with a living host fungus, plate confrontation assays with R. solani and B. cinerea as fungal hosts were performed. During the early phases of the interaction with R. solani, i.e. growth towards the host fungus and establishment of direct contact, the Δste12 mutant behaved similar as the parental strain (Fig. 5 A). After 14 days however, R. solani hyphae were completely lysed by the parental and the complemented strain while only incompletely lysed by the Δste12 mutant. A reduction in the mycoparasitic attack and host lysing abilities of the mutant was also evident against B. cinerea. While the parental and the complemented strain steadily overgrew the host, ste12 deletion resulted in a halt shortly after establishment of contact between the two fungi which could hardly be overcome by the Δste12 mutant even under prolonged incubation times (Fig. 5 A).


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)

Mycoparasitic activity of the Δste12 mutant against R. solani and B. cinerea as hosts.(A) Plate confrontation assays of the Δste12 mutant (second panel), the parental strain (upper panel) and the complemented strains ste12-C1 (third panel) and ste12-C2 (fourth panel) against host fungi. Pictures were taken 1, 2, 3, and 14 days (R. solani) and 7 and 14 days (B. cinerea) after inoculation of the two fungi on opposite sides of the plate. (B) Microscopic analyses of the confrontation zone between T. atroviride (right side) and R. solani (left side). The Δste12 mutant approaches the host as aggregated hyphae with only single hyphae attaching to Rhizoctonia. Attachments to host hyphae are marked by arrows. The scale bar represents 50 µm. (C) Attachment to and coiling around host hyphae. Despite the inability of the Δste12 mutant to fully overgrow and parasitize B. cinerea, the mutant shows the typical mycoparasitism-associated coiling response.
© Copyright Policy
Related In: Results  -  Collection

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

pone-0111636-g005: Mycoparasitic activity of the Δste12 mutant against R. solani and B. cinerea as hosts.(A) Plate confrontation assays of the Δste12 mutant (second panel), the parental strain (upper panel) and the complemented strains ste12-C1 (third panel) and ste12-C2 (fourth panel) against host fungi. Pictures were taken 1, 2, 3, and 14 days (R. solani) and 7 and 14 days (B. cinerea) after inoculation of the two fungi on opposite sides of the plate. (B) Microscopic analyses of the confrontation zone between T. atroviride (right side) and R. solani (left side). The Δste12 mutant approaches the host as aggregated hyphae with only single hyphae attaching to Rhizoctonia. Attachments to host hyphae are marked by arrows. The scale bar represents 50 µm. (C) Attachment to and coiling around host hyphae. Despite the inability of the Δste12 mutant to fully overgrow and parasitize B. cinerea, the mutant shows the typical mycoparasitism-associated coiling response.
Mentions: In order to assess whether Tmk1 regulates the mycoparasitic activity of T. atroviride by employing the Ste12 transcription factor and whether the observed aberrant self-attachment of Δste12 impacts the mycoparasitic interaction with a living host fungus, plate confrontation assays with R. solani and B. cinerea as fungal hosts were performed. During the early phases of the interaction with R. solani, i.e. growth towards the host fungus and establishment of direct contact, the Δste12 mutant behaved similar as the parental strain (Fig. 5 A). After 14 days however, R. solani hyphae were completely lysed by the parental and the complemented strain while only incompletely lysed by the Δste12 mutant. A reduction in the mycoparasitic attack and host lysing abilities of the mutant was also evident against B. cinerea. While the parental and the complemented strain steadily overgrew the host, ste12 deletion resulted in a halt shortly after establishment of contact between the two fungi which could hardly be overcome by the Δste12 mutant even under prolonged incubation times (Fig. 5 A).

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