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A genetic code alteration is a phenotype diversity generator in the human pathogen Candida albicans.

Miranda I, Rocha R, Santos MC, Mateus DD, Moura GR, Carreto L, Santos MA - PLoS ONE (2007)

Bottom Line: We have reconstructed the early stages of the Candida genetic code alteration by engineering tRNAs that partially reverted the identity of serine CUG codons back to their standard leucine meaning.Such genetic code manipulation had profound cellular consequences as it exposed important morphological variation, altered gene expression, re-arranged the karyotype, increased cell-cell adhesion and secretion of hydrolytic enzymes.Our study provides the first experimental evidence for an important role of genetic code alterations as generators of phenotypic diversity of high selective potential and supports the hypothesis that they speed up evolution of new phenotypes.

View Article: PubMed Central - PubMed

Affiliation: Department of Biology, Centro de Estudos do Ambiente e do Mar, University of Aveiro, Aveiro, Portugal.

ABSTRACT

Background: The discovery of genetic code alterations and expansions in both prokaryotes and eukaryotes abolished the hypothesis of a frozen and universal genetic code and exposed unanticipated flexibility in codon and amino acid assignments. It is now clear that codon identity alterations involve sense and non-sense codons and can occur in organisms with complex genomes and proteomes. However, the biological functions, the molecular mechanisms of evolution and the diversity of genetic code alterations remain largely unknown. In various species of the genus Candida, the leucine CUG codon is decoded as serine by a unique serine tRNA that contains a leucine 5'-CAG-3'anticodon (tRNA(CAG)(Ser)). We are using this codon identity redefinition as a model system to elucidate the evolution of genetic code alterations.

Methodology/principal findings: We have reconstructed the early stages of the Candida genetic code alteration by engineering tRNAs that partially reverted the identity of serine CUG codons back to their standard leucine meaning. Such genetic code manipulation had profound cellular consequences as it exposed important morphological variation, altered gene expression, re-arranged the karyotype, increased cell-cell adhesion and secretion of hydrolytic enzymes.

Conclusion/significance: Our study provides the first experimental evidence for an important role of genetic code alterations as generators of phenotypic diversity of high selective potential and supports the hypothesis that they speed up evolution of new phenotypes.

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Related in: MedlinePlus

Increased CUG ambiguity resulted in higher hydrolytic activity and increased adhesion.A) Highly ambiguous cells (pUA15) exhibited strong adhesion phenotypes both in solid and liquid media. Adhesion to the solid agar surface resulted from cell-cell and cell-agar adhesion. In liquid media, cells showed a strong flocculation phenotype and sedimented even when grown with agitation (30°C for 2 days). B–C) Cells transformed with pUA13-14 (data not shown) and with pUA15 plasmids, had higher SAP and phospholipase activity than control cells, as determined by hydrolysis of BSA and egg yolk, respectively. Hydrolytic activity was quantified by measuring precipitation zones formed around the colonies, corrected by the colony diameter, in order to obtain Pz values.
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pone-0000996-g005: Increased CUG ambiguity resulted in higher hydrolytic activity and increased adhesion.A) Highly ambiguous cells (pUA15) exhibited strong adhesion phenotypes both in solid and liquid media. Adhesion to the solid agar surface resulted from cell-cell and cell-agar adhesion. In liquid media, cells showed a strong flocculation phenotype and sedimented even when grown with agitation (30°C for 2 days). B–C) Cells transformed with pUA13-14 (data not shown) and with pUA15 plasmids, had higher SAP and phospholipase activity than control cells, as determined by hydrolysis of BSA and egg yolk, respectively. Hydrolytic activity was quantified by measuring precipitation zones formed around the colonies, corrected by the colony diameter, in order to obtain Pz values.

Mentions: CUG ambiguity also increased cell adhesion in liquid and solid media (Figure 5A), and once more, this phenotype was exacerbated in pUA15 clones, as they displayed strong flocculation in liquid media (Figure 5A). Interestingly, more than 50% of the genes involved in adhesion contain CUG codons. For example, the ALS gene family which encodes cell-surface glycoproteins that mediate adhesion to host surfaces [35], contain various CUG codons (3CUGs-ALS2, ALS3, ALS8; 4CUGs-ALS4; 5CUGs-ALS1; 11CUGs-ALS6; 12CUGs-ALS9; 18CUGs-ALS7). It is not yet clear whether the change of serine (polar) for leucine (hydrophobic) at CUG positions in the Als proteins is responsible for the flocculation and exacerbated agar adhesion observed in pUA15 clones. But, the strong adhesion phenotypes resulting from expression of ALA1, EAP1 and members of the C. albicans ALS gene family, namely ALS1 and ALS5 in S. cerevisiae, support the hypothesis that the replacement of serines with leucines at CUG positions increases adhesion [36]–[41].


A genetic code alteration is a phenotype diversity generator in the human pathogen Candida albicans.

Miranda I, Rocha R, Santos MC, Mateus DD, Moura GR, Carreto L, Santos MA - PLoS ONE (2007)

Increased CUG ambiguity resulted in higher hydrolytic activity and increased adhesion.A) Highly ambiguous cells (pUA15) exhibited strong adhesion phenotypes both in solid and liquid media. Adhesion to the solid agar surface resulted from cell-cell and cell-agar adhesion. In liquid media, cells showed a strong flocculation phenotype and sedimented even when grown with agitation (30°C for 2 days). B–C) Cells transformed with pUA13-14 (data not shown) and with pUA15 plasmids, had higher SAP and phospholipase activity than control cells, as determined by hydrolysis of BSA and egg yolk, respectively. Hydrolytic activity was quantified by measuring precipitation zones formed around the colonies, corrected by the colony diameter, in order to obtain Pz values.
© Copyright Policy
Related In: Results  -  Collection

Show All Figures
getmorefigures.php?uid=PMC1991585&req=5

pone-0000996-g005: Increased CUG ambiguity resulted in higher hydrolytic activity and increased adhesion.A) Highly ambiguous cells (pUA15) exhibited strong adhesion phenotypes both in solid and liquid media. Adhesion to the solid agar surface resulted from cell-cell and cell-agar adhesion. In liquid media, cells showed a strong flocculation phenotype and sedimented even when grown with agitation (30°C for 2 days). B–C) Cells transformed with pUA13-14 (data not shown) and with pUA15 plasmids, had higher SAP and phospholipase activity than control cells, as determined by hydrolysis of BSA and egg yolk, respectively. Hydrolytic activity was quantified by measuring precipitation zones formed around the colonies, corrected by the colony diameter, in order to obtain Pz values.
Mentions: CUG ambiguity also increased cell adhesion in liquid and solid media (Figure 5A), and once more, this phenotype was exacerbated in pUA15 clones, as they displayed strong flocculation in liquid media (Figure 5A). Interestingly, more than 50% of the genes involved in adhesion contain CUG codons. For example, the ALS gene family which encodes cell-surface glycoproteins that mediate adhesion to host surfaces [35], contain various CUG codons (3CUGs-ALS2, ALS3, ALS8; 4CUGs-ALS4; 5CUGs-ALS1; 11CUGs-ALS6; 12CUGs-ALS9; 18CUGs-ALS7). It is not yet clear whether the change of serine (polar) for leucine (hydrophobic) at CUG positions in the Als proteins is responsible for the flocculation and exacerbated agar adhesion observed in pUA15 clones. But, the strong adhesion phenotypes resulting from expression of ALA1, EAP1 and members of the C. albicans ALS gene family, namely ALS1 and ALS5 in S. cerevisiae, support the hypothesis that the replacement of serines with leucines at CUG positions increases adhesion [36]–[41].

Bottom Line: We have reconstructed the early stages of the Candida genetic code alteration by engineering tRNAs that partially reverted the identity of serine CUG codons back to their standard leucine meaning.Such genetic code manipulation had profound cellular consequences as it exposed important morphological variation, altered gene expression, re-arranged the karyotype, increased cell-cell adhesion and secretion of hydrolytic enzymes.Our study provides the first experimental evidence for an important role of genetic code alterations as generators of phenotypic diversity of high selective potential and supports the hypothesis that they speed up evolution of new phenotypes.

View Article: PubMed Central - PubMed

Affiliation: Department of Biology, Centro de Estudos do Ambiente e do Mar, University of Aveiro, Aveiro, Portugal.

ABSTRACT

Background: The discovery of genetic code alterations and expansions in both prokaryotes and eukaryotes abolished the hypothesis of a frozen and universal genetic code and exposed unanticipated flexibility in codon and amino acid assignments. It is now clear that codon identity alterations involve sense and non-sense codons and can occur in organisms with complex genomes and proteomes. However, the biological functions, the molecular mechanisms of evolution and the diversity of genetic code alterations remain largely unknown. In various species of the genus Candida, the leucine CUG codon is decoded as serine by a unique serine tRNA that contains a leucine 5'-CAG-3'anticodon (tRNA(CAG)(Ser)). We are using this codon identity redefinition as a model system to elucidate the evolution of genetic code alterations.

Methodology/principal findings: We have reconstructed the early stages of the Candida genetic code alteration by engineering tRNAs that partially reverted the identity of serine CUG codons back to their standard leucine meaning. Such genetic code manipulation had profound cellular consequences as it exposed important morphological variation, altered gene expression, re-arranged the karyotype, increased cell-cell adhesion and secretion of hydrolytic enzymes.

Conclusion/significance: Our study provides the first experimental evidence for an important role of genetic code alterations as generators of phenotypic diversity of high selective potential and supports the hypothesis that they speed up evolution of new phenotypes.

Show MeSH
Related in: MedlinePlus