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Tec1 mediates the pheromone response of the white phenotype of Candida albicans: insights into the evolution of new signal transduction pathways.

Sahni N, Yi S, Daniels KJ, Huang G, Srikantha T, Soll DR - PLoS Biol. (2010)

Bottom Line: The three portions of this new regulatory pathway appear to have been derived from three different ancestral programs still functional in C. albicans.The upstream portion, including signals, receptors, the trimeric G protein complex, and the MAP kinase cascade, was derived intact from the upstream portion of the opaque pheromone response pathway of the mating process; Tec1, the transcription factor targeted by the MAP kinase pathway, was derived from a filamentation pathway; and the white-specific downstream target genes were derived from an ancestral biofilm process.The evolution of this pheromone response pathway provides a possible paradigm for how such signal transduction pathways evolve.

View Article: PubMed Central - PubMed

Affiliation: Department of Biology, The University of Iowa, Iowa City, Iowa, United States of America.

ABSTRACT
The way in which signal transduction pathways evolve remains a mystery, primarily because we have few examples of ones that have newly evolved. There are numerous examples of how signal transduction pathways in the same organism selectively share components, most notably between the signal transduction pathways in Saccharomyces cerevisiae for the mating process, the filamentation process, cell wall integrity, ascospore formation, and osmoregulation. These examples, however, have not provided insights into how such pathways evolve. Here, through construction of an overexpression library for 107 transcription factors, and through mutational analyses, we have identified the transcription factor Tec1 as the last component of the newly evolved signal transduction pathway that regulates the pheromone response of the white cell phenotype in Candida albicans. The elucidation of this last component, Tec1, establishes a comprehensive description of the pheromone response pathway in the white cell phenotype of C. albicans, providing a unique perspective on how new signal transduction pathways may evolve. The three portions of this new regulatory pathway appear to have been derived from three different ancestral programs still functional in C. albicans. The upstream portion, including signals, receptors, the trimeric G protein complex, and the MAP kinase cascade, was derived intact from the upstream portion of the opaque pheromone response pathway of the mating process; Tec1, the transcription factor targeted by the MAP kinase pathway, was derived from a filamentation pathway; and the white-specific downstream target genes were derived from an ancestral biofilm process. The evolution of this pheromone response pathway provides a possible paradigm for how such signal transduction pathways evolve.

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Tec1 functions downstream of the MAP kinase cascade.Up-regulation of TEC1 by α-pheromone requires the α-pheromone receptor, trimeric G protein complex, and MAP kinase cascade. (A) Northern analysis of pheromone (α-ph) induction of TEC1 in P37005 white (Wh) and opaque (Op) cells, and in white cells of the mutants ste2/ste2, ste4/ste4, and cek1/cek1 cek2/cek2. (B) Overexpression of STE11 induces adhesion in the absence of α-pheromone. Overexpression was induced in white cells by adding 50 µg per ml of doxycycline (Dox) to the overexpression strain P37005-TETp-STE11. (C) Overexpression of STE11 by addition of 50 µg per ml of doxycycline in the absence of α-pheromone activates genes in the white response pathway in strain P37005-TETp-STE11. (D) Western blot analysis of Tec1-GFP using anti-GFP antibody in strain tec1/tec1-TEC1 in which TEC1 is tagged with GFP.
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pbio-1000363-g002: Tec1 functions downstream of the MAP kinase cascade.Up-regulation of TEC1 by α-pheromone requires the α-pheromone receptor, trimeric G protein complex, and MAP kinase cascade. (A) Northern analysis of pheromone (α-ph) induction of TEC1 in P37005 white (Wh) and opaque (Op) cells, and in white cells of the mutants ste2/ste2, ste4/ste4, and cek1/cek1 cek2/cek2. (B) Overexpression of STE11 induces adhesion in the absence of α-pheromone. Overexpression was induced in white cells by adding 50 µg per ml of doxycycline (Dox) to the overexpression strain P37005-TETp-STE11. (C) Overexpression of STE11 by addition of 50 µg per ml of doxycycline in the absence of α-pheromone activates genes in the white response pathway in strain P37005-TETp-STE11. (D) Western blot analysis of Tec1-GFP using anti-GFP antibody in strain tec1/tec1-TEC1 in which TEC1 is tagged with GFP.

Mentions: To test whether TEC1 expression was regulated by α-pheromone and the MAP kinase pathway, a northern analysis was performed to assess its expression in deletion mutants for key elements of the signal transduction pathway in the absence and presence of α-pheromone. In white cells of the control strain P37005, TEC1 was expressed at a basal level in the absence of α-pheromone, but at a highly elevated level in the presence of α-pheromone (Figure 2A). In opaque cells of P37005, TEC1 was expressed at the same basal level in the absence and presence of α-pheromone, demonstrating that unlike white cells, α-pheromone did not up-regulate TEC1 transcription in opaque cells (Figure 2A). In white cells of the deletion mutants of STE2, which encodes the α-pheromone receptor, and STE4, which encodes the beta subunit of the heterotrimeric G protein complex, and in white cells of the double mutant for CEK1 and CEK2, which encode the two MAP kinase isoforms (ste2/ste2, ste4/ste4, cek1/cek1 cek2/cek2, respectively), α-pheromone did not up-regulate TEC1 (Figure 2A). Hyperactivating the MAP kinase pathway by overexpressing STE11, which encodes the first component of the MAP kinase cascade, in white cells of strain P37005-TETp-STE11 in the absence of α-pheromone, caused an increase in adhesion of over 100-fold (Figure 2B) and up-regulation of TEC1 transcription (Figure 2C). Overexpression of STE11 in the absence of α-pheromone also up-regulated CEK1, CEK2, CSH1, and PBR1 (Figure 2C), genes previously shown to be up-regulated by α-pheromone through the MAP kinase pathway [10],[23]. Overexpression of STE11 in white cells did not up-regulate opaque-specific genes (unpublished data).


Tec1 mediates the pheromone response of the white phenotype of Candida albicans: insights into the evolution of new signal transduction pathways.

Sahni N, Yi S, Daniels KJ, Huang G, Srikantha T, Soll DR - PLoS Biol. (2010)

Tec1 functions downstream of the MAP kinase cascade.Up-regulation of TEC1 by α-pheromone requires the α-pheromone receptor, trimeric G protein complex, and MAP kinase cascade. (A) Northern analysis of pheromone (α-ph) induction of TEC1 in P37005 white (Wh) and opaque (Op) cells, and in white cells of the mutants ste2/ste2, ste4/ste4, and cek1/cek1 cek2/cek2. (B) Overexpression of STE11 induces adhesion in the absence of α-pheromone. Overexpression was induced in white cells by adding 50 µg per ml of doxycycline (Dox) to the overexpression strain P37005-TETp-STE11. (C) Overexpression of STE11 by addition of 50 µg per ml of doxycycline in the absence of α-pheromone activates genes in the white response pathway in strain P37005-TETp-STE11. (D) Western blot analysis of Tec1-GFP using anti-GFP antibody in strain tec1/tec1-TEC1 in which TEC1 is tagged with GFP.
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getmorefigures.php?uid=PMC2864266&req=5

pbio-1000363-g002: Tec1 functions downstream of the MAP kinase cascade.Up-regulation of TEC1 by α-pheromone requires the α-pheromone receptor, trimeric G protein complex, and MAP kinase cascade. (A) Northern analysis of pheromone (α-ph) induction of TEC1 in P37005 white (Wh) and opaque (Op) cells, and in white cells of the mutants ste2/ste2, ste4/ste4, and cek1/cek1 cek2/cek2. (B) Overexpression of STE11 induces adhesion in the absence of α-pheromone. Overexpression was induced in white cells by adding 50 µg per ml of doxycycline (Dox) to the overexpression strain P37005-TETp-STE11. (C) Overexpression of STE11 by addition of 50 µg per ml of doxycycline in the absence of α-pheromone activates genes in the white response pathway in strain P37005-TETp-STE11. (D) Western blot analysis of Tec1-GFP using anti-GFP antibody in strain tec1/tec1-TEC1 in which TEC1 is tagged with GFP.
Mentions: To test whether TEC1 expression was regulated by α-pheromone and the MAP kinase pathway, a northern analysis was performed to assess its expression in deletion mutants for key elements of the signal transduction pathway in the absence and presence of α-pheromone. In white cells of the control strain P37005, TEC1 was expressed at a basal level in the absence of α-pheromone, but at a highly elevated level in the presence of α-pheromone (Figure 2A). In opaque cells of P37005, TEC1 was expressed at the same basal level in the absence and presence of α-pheromone, demonstrating that unlike white cells, α-pheromone did not up-regulate TEC1 transcription in opaque cells (Figure 2A). In white cells of the deletion mutants of STE2, which encodes the α-pheromone receptor, and STE4, which encodes the beta subunit of the heterotrimeric G protein complex, and in white cells of the double mutant for CEK1 and CEK2, which encode the two MAP kinase isoforms (ste2/ste2, ste4/ste4, cek1/cek1 cek2/cek2, respectively), α-pheromone did not up-regulate TEC1 (Figure 2A). Hyperactivating the MAP kinase pathway by overexpressing STE11, which encodes the first component of the MAP kinase cascade, in white cells of strain P37005-TETp-STE11 in the absence of α-pheromone, caused an increase in adhesion of over 100-fold (Figure 2B) and up-regulation of TEC1 transcription (Figure 2C). Overexpression of STE11 in the absence of α-pheromone also up-regulated CEK1, CEK2, CSH1, and PBR1 (Figure 2C), genes previously shown to be up-regulated by α-pheromone through the MAP kinase pathway [10],[23]. Overexpression of STE11 in white cells did not up-regulate opaque-specific genes (unpublished data).

Bottom Line: The three portions of this new regulatory pathway appear to have been derived from three different ancestral programs still functional in C. albicans.The upstream portion, including signals, receptors, the trimeric G protein complex, and the MAP kinase cascade, was derived intact from the upstream portion of the opaque pheromone response pathway of the mating process; Tec1, the transcription factor targeted by the MAP kinase pathway, was derived from a filamentation pathway; and the white-specific downstream target genes were derived from an ancestral biofilm process.The evolution of this pheromone response pathway provides a possible paradigm for how such signal transduction pathways evolve.

View Article: PubMed Central - PubMed

Affiliation: Department of Biology, The University of Iowa, Iowa City, Iowa, United States of America.

ABSTRACT
The way in which signal transduction pathways evolve remains a mystery, primarily because we have few examples of ones that have newly evolved. There are numerous examples of how signal transduction pathways in the same organism selectively share components, most notably between the signal transduction pathways in Saccharomyces cerevisiae for the mating process, the filamentation process, cell wall integrity, ascospore formation, and osmoregulation. These examples, however, have not provided insights into how such pathways evolve. Here, through construction of an overexpression library for 107 transcription factors, and through mutational analyses, we have identified the transcription factor Tec1 as the last component of the newly evolved signal transduction pathway that regulates the pheromone response of the white cell phenotype in Candida albicans. The elucidation of this last component, Tec1, establishes a comprehensive description of the pheromone response pathway in the white cell phenotype of C. albicans, providing a unique perspective on how new signal transduction pathways may evolve. The three portions of this new regulatory pathway appear to have been derived from three different ancestral programs still functional in C. albicans. The upstream portion, including signals, receptors, the trimeric G protein complex, and the MAP kinase cascade, was derived intact from the upstream portion of the opaque pheromone response pathway of the mating process; Tec1, the transcription factor targeted by the MAP kinase pathway, was derived from a filamentation pathway; and the white-specific downstream target genes were derived from an ancestral biofilm process. The evolution of this pheromone response pathway provides a possible paradigm for how such signal transduction pathways evolve.

Show MeSH
Related in: MedlinePlus