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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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Related in: MedlinePlus

Expression levels of ldcA and rlpA in the bacteriocyte. Ivory columns, expression levels in the whole body; blue columns, expression levels in the bacteriocyte; bars, standard errors (n = 6). The expression levels are shown in terms of mRNA copies of target genes per copy of mRNA for RpL7. Asterisks indicate statistically significant differences (Mann-Whitney U-test; **, p < 0.01).
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Figure 5: Expression levels of ldcA and rlpA in the bacteriocyte. Ivory columns, expression levels in the whole body; blue columns, expression levels in the bacteriocyte; bars, standard errors (n = 6). The expression levels are shown in terms of mRNA copies of target genes per copy of mRNA for RpL7. Asterisks indicate statistically significant differences (Mann-Whitney U-test; **, p < 0.01).

Mentions: To examine the expression profiles of ldcA and rlpA, we quantified their transcripts in the bacteriocyte and in the whole body using real-time quantitative RT-PCR (Figure 5). The results clearly demonstrated that ldcA and rlpA are actively transcribed in the bacteriocyte. Transcripts for ldcA and rlpA were 11.6 and 154-fold more abundant in the bacteriocyte than in the whole body, respectively. It is also notable that the copy numbers of their transcripts in the bacteriocyte were comparable to those of the control transcript encoding ribosomal protein L7 (RpL7), indicating that their expression levels are relatively high. High levels of expression of these genes in the bacteriocyte strongly suggest that they are not only functional, but they play important roles in maintaining the symbiotic relationship with the obligate mutualist, Buchnera.


Aphids acquired symbiotic genes via lateral gene transfer.

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

Expression levels of ldcA and rlpA in the bacteriocyte. Ivory columns, expression levels in the whole body; blue columns, expression levels in the bacteriocyte; bars, standard errors (n = 6). The expression levels are shown in terms of mRNA copies of target genes per copy of mRNA for RpL7. Asterisks indicate statistically significant differences (Mann-Whitney U-test; **, p < 0.01).
© Copyright Policy - open-access
Related In: Results  -  Collection

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

Figure 5: Expression levels of ldcA and rlpA in the bacteriocyte. Ivory columns, expression levels in the whole body; blue columns, expression levels in the bacteriocyte; bars, standard errors (n = 6). The expression levels are shown in terms of mRNA copies of target genes per copy of mRNA for RpL7. Asterisks indicate statistically significant differences (Mann-Whitney U-test; **, p < 0.01).
Mentions: To examine the expression profiles of ldcA and rlpA, we quantified their transcripts in the bacteriocyte and in the whole body using real-time quantitative RT-PCR (Figure 5). The results clearly demonstrated that ldcA and rlpA are actively transcribed in the bacteriocyte. Transcripts for ldcA and rlpA were 11.6 and 154-fold more abundant in the bacteriocyte than in the whole body, respectively. It is also notable that the copy numbers of their transcripts in the bacteriocyte were comparable to those of the control transcript encoding ribosomal protein L7 (RpL7), indicating that their expression levels are relatively high. High levels of expression of these genes in the bacteriocyte strongly suggest that they are not only functional, but they play important roles in maintaining the symbiotic relationship with the obligate mutualist, Buchnera.

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