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Aphids acquired symbiotic genes via lateral gene transfer.

Nikoh N, Nakabachi A - BMC Biol. (2009)

Bottom Line: Sequence similarity searches demonstrated that these fully sequenced transcripts are significantly similar to the bacterial genes ldcA (product, LD-carboxypeptidase) and rlpA (product, rare lipoprotein A), respectively.Real-time quantitative RT-PCR demonstrated that ldcA and rlpA are expressed 11.6 and 154-fold higher in the bacteriocyte than in the whole body, respectively.LdcA is an enzyme required for recycling murein (peptidoglycan), which is a component of the bacterial cell wall.

View Article: PubMed Central - HTML - PubMed

Affiliation: Division of Natural Sciences, The Open University of Japan, Chiba, Japan. nikoh@u-air.ac.jp

ABSTRACT

Background: Aphids possess bacteriocytes, which are cells specifically differentiated to harbour the obligate mutualist Buchnera aphidicola (gamma-Proteobacteria). Buchnera has lost many of the genes that appear to be essential for bacterial life. From the bacteriocyte of the pea aphid Acyrthosiphon pisum, we previously identified two clusters of expressed sequence tags that display similarity only to bacterial genes. Southern blot analysis demonstrated that they are encoded in the aphid genome. In this study, in order to assess the possibility of lateral gene transfer, we determined the full-length sequences of these transcripts, and performed detailed structural and phylogenetic analyses. We further examined their expression levels in the bacteriocyte using real-time quantitative RT-PCR.

Results: Sequence similarity searches demonstrated that these fully sequenced transcripts are significantly similar to the bacterial genes ldcA (product, LD-carboxypeptidase) and rlpA (product, rare lipoprotein A), respectively. Buchnera lacks these genes, whereas many other bacteria, including Escherichia coli, a close relative of Buchnera, possess both ldcA and rlpA. Molecular phylogenetic analysis clearly demonstrated that the aphid ldcA was derived from a rickettsial bacterium closely related to the extant Wolbachia spp. (alpha-Proteobacteria, Rickettsiales), which are intracellular symbionts of various lineages of arthropods. The evolutionary origin of rlpA was not fully resolved, but it was clearly demonstrated that its double-psi beta-barrel domain is of bacterial origin. Real-time quantitative RT-PCR demonstrated that ldcA and rlpA are expressed 11.6 and 154-fold higher in the bacteriocyte than in the whole body, respectively. LdcA is an enzyme required for recycling murein (peptidoglycan), which is a component of the bacterial cell wall. As Buchnera possesses a cell wall composed of murein but lacks ldcA, a high level of expression of the aphid ldcA in the bacteriocyte may be essential to maintain Buchnera. Although the function of RlpA is not well known, conspicuous up-regulation of the aphid rlpA in the bacteriocyte implies that this gene is also essential for Buchnera.

Conclusion: In this study, we obtained several lines of evidence indicating that aphids acquired genes from bacteria via lateral gene transfer and that these genes are used to maintain the obligately mutualistic bacterium, Buchnera.

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Structure of the aphid LdcA. (A) ClustalX alignment of amino acid sequences of LdcAs. Residues conserved in all lineages, four lineages, and three lineages are shaded black, dark gray, and light gray, respectively. Arrowheads indicate the residues required for LdcA activity. The long form of the aphid LdcA is used for the alignment. (B) Domain structure of the aphid LdcA protein and structures of the corresponding mRNA and genomic DNA.
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Figure 1: Structure of the aphid LdcA. (A) ClustalX alignment of amino acid sequences of LdcAs. Residues conserved in all lineages, four lineages, and three lineages are shaded black, dark gray, and light gray, respectively. Arrowheads indicate the residues required for LdcA activity. The long form of the aphid LdcA is used for the alignment. (B) Domain structure of the aphid LdcA protein and structures of the corresponding mRNA and genomic DNA.

Mentions: In the previous study, the sequences of the transcripts corresponding to the cDNA clusters (unigenes) R2C00193 and R2C00214 were not fully determined, as the cap-trapper cDNA clones were sequenced only from the 5' end. In the present study, all the cap-trapper clone inserts relevant to these unigenes were amplified by PCR using vector primers (T3 and T7) and sequenced from both ends to obtain full-length sequences. In the case of R2C00214, all of the four clones had an identical sequence of 1312 bp encoding a polypeptide of 226 amino acid residues (Figure 1). Full-length sequences for R2C00193 were approximately 1 kb in length, with slight variations mainly in the putative untranslated regions (UTRs). They encoded a polypeptide of 220 amino acid residues (Figure 2). These full-length unigenes are hereafter referred to as R2C00214F (DDBJ: AB435382) and R2C00193F (DDBJ: AB435384 and AB435385), respectively.


Aphids acquired symbiotic genes via lateral gene transfer.

Nikoh N, Nakabachi A - BMC Biol. (2009)

Structure of the aphid LdcA. (A) ClustalX alignment of amino acid sequences of LdcAs. Residues conserved in all lineages, four lineages, and three lineages are shaded black, dark gray, and light gray, respectively. Arrowheads indicate the residues required for LdcA activity. The long form of the aphid LdcA is used for the alignment. (B) Domain structure of the aphid LdcA protein and structures of the corresponding mRNA and genomic DNA.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC2662799&req=5

Figure 1: Structure of the aphid LdcA. (A) ClustalX alignment of amino acid sequences of LdcAs. Residues conserved in all lineages, four lineages, and three lineages are shaded black, dark gray, and light gray, respectively. Arrowheads indicate the residues required for LdcA activity. The long form of the aphid LdcA is used for the alignment. (B) Domain structure of the aphid LdcA protein and structures of the corresponding mRNA and genomic DNA.
Mentions: In the previous study, the sequences of the transcripts corresponding to the cDNA clusters (unigenes) R2C00193 and R2C00214 were not fully determined, as the cap-trapper cDNA clones were sequenced only from the 5' end. In the present study, all the cap-trapper clone inserts relevant to these unigenes were amplified by PCR using vector primers (T3 and T7) and sequenced from both ends to obtain full-length sequences. In the case of R2C00214, all of the four clones had an identical sequence of 1312 bp encoding a polypeptide of 226 amino acid residues (Figure 1). Full-length sequences for R2C00193 were approximately 1 kb in length, with slight variations mainly in the putative untranslated regions (UTRs). They encoded a polypeptide of 220 amino acid residues (Figure 2). These full-length unigenes are hereafter referred to as R2C00214F (DDBJ: AB435382) and R2C00193F (DDBJ: AB435384 and AB435385), respectively.

Bottom Line: Sequence similarity searches demonstrated that these fully sequenced transcripts are significantly similar to the bacterial genes ldcA (product, LD-carboxypeptidase) and rlpA (product, rare lipoprotein A), respectively.Real-time quantitative RT-PCR demonstrated that ldcA and rlpA are expressed 11.6 and 154-fold higher in the bacteriocyte than in the whole body, respectively.LdcA is an enzyme required for recycling murein (peptidoglycan), which is a component of the bacterial cell wall.

View Article: PubMed Central - HTML - PubMed

Affiliation: Division of Natural Sciences, The Open University of Japan, Chiba, Japan. nikoh@u-air.ac.jp

ABSTRACT

Background: Aphids possess bacteriocytes, which are cells specifically differentiated to harbour the obligate mutualist Buchnera aphidicola (gamma-Proteobacteria). Buchnera has lost many of the genes that appear to be essential for bacterial life. From the bacteriocyte of the pea aphid Acyrthosiphon pisum, we previously identified two clusters of expressed sequence tags that display similarity only to bacterial genes. Southern blot analysis demonstrated that they are encoded in the aphid genome. In this study, in order to assess the possibility of lateral gene transfer, we determined the full-length sequences of these transcripts, and performed detailed structural and phylogenetic analyses. We further examined their expression levels in the bacteriocyte using real-time quantitative RT-PCR.

Results: Sequence similarity searches demonstrated that these fully sequenced transcripts are significantly similar to the bacterial genes ldcA (product, LD-carboxypeptidase) and rlpA (product, rare lipoprotein A), respectively. Buchnera lacks these genes, whereas many other bacteria, including Escherichia coli, a close relative of Buchnera, possess both ldcA and rlpA. Molecular phylogenetic analysis clearly demonstrated that the aphid ldcA was derived from a rickettsial bacterium closely related to the extant Wolbachia spp. (alpha-Proteobacteria, Rickettsiales), which are intracellular symbionts of various lineages of arthropods. The evolutionary origin of rlpA was not fully resolved, but it was clearly demonstrated that its double-psi beta-barrel domain is of bacterial origin. Real-time quantitative RT-PCR demonstrated that ldcA and rlpA are expressed 11.6 and 154-fold higher in the bacteriocyte than in the whole body, respectively. LdcA is an enzyme required for recycling murein (peptidoglycan), which is a component of the bacterial cell wall. As Buchnera possesses a cell wall composed of murein but lacks ldcA, a high level of expression of the aphid ldcA in the bacteriocyte may be essential to maintain Buchnera. Although the function of RlpA is not well known, conspicuous up-regulation of the aphid rlpA in the bacteriocyte implies that this gene is also essential for Buchnera.

Conclusion: In this study, we obtained several lines of evidence indicating that aphids acquired genes from bacteria via lateral gene transfer and that these genes are used to maintain the obligately mutualistic bacterium, Buchnera.

Show MeSH
Related in: MedlinePlus