MyLo Ly Thao

Cospeciation of psyllids and their primary prokaryotic endosymbionts.

ABSTRACT Psyllids are plant sap-feeding insects that harbor prokaryotic endosymbionts in specialized cells within the body cavity. Four-kilobase DNA fragments containing 16S and 23S ribosomal DNA (rDNA) were amplified from the primary (P) endosymbiont of 32 species of psyllids representing three psyllid families and eight subfamilies. In addition, 0.54-kb fragments of the psyllid nuclear genewingless were also amplified from 26 species. Phylogenetic trees derived from 16S-23S rDNA and from the host winglessgene are very similar, and tests of compatibility of the data sets show no significant conflict between host and endosymbiont phylogenies. This result is consistent with a single infection of a shared psyllid ancestor and subsequent cospeciation of the host and the endosymbiont. In addition, the phylogenies based on DNA sequences generally agreed with psyllid taxonomy based on morphology. The 3′ end of the 16S rDNA of the P endosymbionts differs from that of other members of the domainBacteria in the lack of a sequence complementary to the mRNA ribosome binding site. The rate of sequence change in the 16S-23S rDNA of the psyllid P endosymbiont was considerably higher than that of other bacteria, including other fast-evolving insect endosymbionts. The lineage consisting of the P endosymbionts of psyllids was given the designation Candidatus Carsonella (gen. nov.) with a single species, Candidatus Carsonella ruddii (sp. nov.).

Evolutionary relationships of primary prokaryotic endosymbionts of whiteflies and their hosts.

ABSTRACT Whiteflies (Hemiptera: Sternorrhyncha: Aleyrodidae) are plant sap-sucking insects that harbor prokaryotic primary endosymbionts (P-endosymbionts) within specialized cells located in their body cavity. Four-kilobase DNA fragments containing 16S-23S ribosomal DNA (rDNA) were amplified from the P-endosymbiont of 24 whiteflies from 22 different species of 2 whitefly subfamilies. In addition, 3-kb DNA fragments containing mitochondrial cytB, nd1, and large-subunit rDNA (LrDNA) were amplified from 17 whitefly species. Comparisons of the P-endosymbiont (16S-23S rDNA) and host (cytB-nd1-LrDNA) phylogenetic trees indicated overall congruence consistent with a single infection of a whitefly ancestor with a bacterium and subsequent cospeciation (cocladogenesis) of the host and the P-endosymbiont. On the basis of both the P-endosymbiont and host trees, the whiteflies could be subdivided into at least five clusters. The major subdivision was between the subfamilies Aleyrodinae and Aleurodicinae. Unlike the P-endosymbionts of may other insects, the P-endosymbionts of whiteflies were related to Pseudomonas and possibly to the P-endosymbionts of psyllids. The lineage consisting of the P-endosymbionts of whiteflies is given the designation “Candidatus Portiera” gen. nov., with a single species, “Candidatus Portiera aleyrodidarum” sp. nov.

Evidence for multiple acquisition of Arsenophonus by whitefly species (Sternorrhyncha: Aleyrodidae)

Whiteflies contain primary prokaryotic endosymbionts located within specialized host cells. This endosymbiotic association is the result of a single infection of the host followed by vertical transmission of the endosymbiont to the progeny. Whiteflies may also be associated with other bacteria called secondary (S-) endosymbionts. The nucleotide sequence of the 16S–23S ribosomal DNA from S-endosymbionts of 13 whitefly species was determined. A phylogenetic analysis of these sequences indicated their grouping into two major clusters, one consisting of two S-endosymbionts related to previously described T-type endosymbionts. The second cluster contained the 16S–23S rDNA sequence of the type strain of Arsenophonus nasoniae as well as sequences of S-endosymbionts from 11 whitefly species. This Arsenophonus cluster contained four S-endosymbionts with intervening sequences of 70–184 nucleotides in their 23S rDNAs. The phylogenetic tree of the Arsenophonus cluster differed greatly from the phylogenetic tree of the primary endosymbionts. These results suggest that, unlike the primary endosymbiont, Arsenophonus may infect whiteflies multiple times and may also be horizontally transmitted.

Organization of the mitochondrial genomes of whiteflies, aphids, and psyllids (Hemiptera, Sternorrhyncha)

BackgroundWith some exceptions, mitochondria within the class Insecta have the same gene content, and generally, a similar gene order allowing the proposal of an ancestral gene order. The principal exceptions are several orders within the Hemipteroid assemblage including the order Thysanoptera, a sister group of the order Hemiptera. Within the Hemiptera, there are available a number of completely sequenced mitochondrial genomes that have a gene order similar to that of the proposed ancestor. None, however, are available from the suborder Sternorryncha that includes whiteflies, psyllids and aphids.ResultsWe have determined the complete nucleotide sequence of the mitochondrial genomes of six species of whiteflies, one psyllid and one aphid. Two species of whiteflies, one psyllid and one aphid have mitochondrial genomes with a gene order very similar to that of the proposed insect ancestor. The remaining four species of whiteflies had variations in the gene order. In all cases, there was the excision of a DNA fragment encoding for cytochrome oxidase subunit III(COIII)-tRNAgly-NADH dehydrogenase subunit 3(ND3)-tRNAala-tRNAarg-tRNAasn from the ancestral position between genes for ATP synthase subunit 6 and NADH dehydrogenase subunit 5. Based on the position in which all or part of this fragment was inserted, the mitochondria could be subdivided into four different gene arrangement types. PCR amplification spanning from COIII to genes outside the inserted region and sequence determination of the resulting fragments, indicated that different whitefly species could be placed into one of these arrangement types. A phylogenetic analysis of 19 whitefly species based on genes for mitochondrial cytochrome b, NADH dehydrogenase subunit 1, and 16S ribosomal DNA as well as cospeciating endosymbiont 16S and 23S ribosomal DNA indicated a clustering of species that corresponded to the gene arrangement types.ConclusionsIn whiteflies, the region of the mitochondrial genome consisting of genes encoding for COIII-tRNAgly-ND3-tRNAala-tRNAarg-tRNAasncan be transposed from its ancestral position to four different locations on the mitochondrial genome. Related species within clusters established by phylogenetic analysis of host and endosymbiont genes have the same mitochondrial gene arrangement indicating a transposition in the ancestor of these clusters.

Secondary (γ-Proteobacteria) Endosymbionts Infect the Primary (β-Proteobacteria) Endosymbionts of Mealybugs Multiple Times and Coevolve with Their Hosts

ABSTRACT Mealybugs (Hemiptera, Coccoidea, Pseudococcidae) are plant sap-sucking insects that have within their body cavities specialized cells containing prokaryotic primary endosymbionts (P-endosymbionts). The P-endosymbionts have the unusual property of containing within their cytoplasm prokaryotic secondary endosymbionts (S-endosymbionts) [C. D. von Dohlen, S. Kohler, S. T. Alsop, and W. R. McManus, Nature (London) 412:433-436, 2001]. Four-kilobase fragments containing 16S-23S ribosomal DNA (rDNA) were obtained from the P-endosymbionts of 22 mealybug species and the S-endosymbionts of 12 representative species. Phylogenetic analyses of the P-endosymbionts indicated that they have a monophyletic origin and are members of the β-subdivision of the Proteobacteria; these organisms were subdivided into five different clusters. The S-endosymbionts were members of the γ-subdivision of the Proteobacteria and were grouped into clusters similar to those observed with the P-endosymbionts. The S-endosymbiont clusters were distinct from each other and from other insect-associated bacteria. The similarity of the clusters formed by the P- and S-endosymbionts suggests that the P-endosymbionts of mealybugs were infected multiple times with different precursors of the S-endosymbionts and once the association was established, the P- and S-endosymbionts were transmitted together. The lineage consisting of the P-endosymbionts of mealybugs was given the designation “Candidatus Tremblaya” gen. nov., with a single species, “Candidatus Tremblaya princeps” sp. nov. The results of phylogenetic analyses of mitochondrial DNA fragments encoding cytochrome oxidase subunits I and II from four representative mealybug species were in agreement with the results of 16S-23S rDNA analyses, suggesting that relationships among strains of “Candidatus T. princeps” are useful in inferring the phylogeny of their mealybug hosts.

Secondary endosymbionts of psyllids have been acquired multiple times

Previous studies have established that psyllids (Hemiptera, Psylloidea) contain primary endosymbionts, designated as Carsonella ruddii, which cospeciate with the psyllid host. This association appears to be the consequence of a single infection of a psyllid ancestor with a bacterium. Some psyllids may have additional secondary (S-) endosymbionts. We have cloned and sequenced the 16S–23S ribosomal RNA genes of seven representative psyllid S-endosymbionts. Comparison of the S-endosymbiont phylogenetic trees with those of C. ruddii indicates a lack of congruence, a finding consistent with multiple infections of psyllids with different precursors of the S-endosymbionts and/or possible horizontal transmission. Additional comparisons indicate that the S-endosymbionts are related to members of the Enterobacteriaceae as well as to several other endosymbionts and insect-associated bacteria.

Phylogenetic evidence for two new insect-associated Chlamydia of the family Simkaniaceae.

On the basis of 16S–23S ribosomal DNA analyses, the whitefly Bemisia tabaci (Sternorrhyncha, Aleyrodidae) and the eriococcid Eriococcus spurius (Sternorrhyncha, Eriococcidae) were each found to harbor novel related chlamydial species within the family Simkaniaceae. The generic designation Fritschea gen. nov. is proposed to accommodate the two species, F. bemisiae sp. nov. and F. eriococci sp. nov. The finding of chlamydial 16S–23S ribosomal DNA in B. tabaci is consistent with a previous electron microscopy study which found that bacteriocytes of this species contain structures that we consider to resemble the elementary and reticulate bodies of chlamydia (Costa HS, Westcot DM, Ullman DE, Rosell R, Brown JK, Johnson MW. Protoplasma 189:194–202, 1995). The cloning and sequencing of a 16.6 kilobase DNA fragment from F. bemisiae indicated that it contains six genes encoding for proteins similar to those found in other species of chlamydia. These results extend the range of organisms that harbor chlamydia.

Genetic Characterization of Plasmids Containing Genes Encoding Enzymes of Leucine Biosynthesis in Endosymbionts (Buchnera) of Aphids

Abstract. The prokaryotic endosymbionts (Buchnera) of aphids are known to provision their hosts with amino acids that are limiting in the aphid diet. Buchnera from the aphids Schizaphis graminum and Diuraphis noxia have plasmids containing leuABCD, genes that encode enzymes of the leucine biosynthetic pathway, as well as genes encoding proteins probably involved in plasmid replication (repA1 and repA2) and an open reading frame (ORF1) of unknown function. The newly reported plasmids closely resemble a plasmid previously described in Buchnera of the aphid Rhopalosiphum padi [Bracho AM, Martínez-Torres D, Moya A, Latorre A (1995) J Mol Evol 41:67–73]. Nucleotide sequence comparisons indicate conserved regions which may correspond to an origin of replication and two promoters, as well as inverted repeats, one of which resembles a rho-independent terminator. Phylogenetic analyses based on amino acid sequences of leu gene products and ORF1 resulted in trees identical to those obtained from endosymbiont chromosomal genes and the plasmid-borne trpEG. These results are consistent with a single evolutionary origin of the leuABCD-containing plasmid in a common ancestor of Aphididae and the lack of plasmid exchange between endosymbionts of different aphid species. Trees for ORF1 and repA (based on both nucleotides and amino acids) are used to examine the basis for leu plasmid differences between Buchnera of Thelaxes suberi and Aphididae. The most plausible explanation is that a single transfer of the leu genes to an ancestral replicon was followed by rearrangements. The related replicon in Buchnera of Pemphigidae, which lacks leuABCD, appears to represent the ancestral condition, implying that the plasmid location of the leu genes arose after the Pemphigidae diverged from other aphid families. This conclusion parallels previously published observations for the unrelated trpEG plasmid, which is present in Aphididae and absent in Pemphigidae. Recruitment of amino acid biosynthetic genes to plasmids has been ongoing in Buchnera lineages after the infection of aphid hosts.

The Genetic Properties of the Primary Endosymbionts of Mealybugs Differ from Those of Other Endosymbionts of Plant Sap-Sucking Insects

ABSTRACT Mealybugs (Hemiptera, Coccoidea, Pseudococcidae), like aphids and psyllids, are plant sap-sucking insects that have an obligate association with prokaryotic endosymbionts that are acquired through vertical, maternal transmission. We sequenced two fragments of the genome of Tremblaya princeps, the endosymbiont of mealybugs, which is a member of the β subdivision of the Proteobacteria. Each of the fragments (35 and 30 kb) contains a copy of 16S-23S-5S rRNA genes. A total of 37 open reading frames were detected, which corresponded to putative rRNA proteins, chaperones, and enzymes of branched-chain amino acid biosynthesis, DNA replication, protein translation, and RNA synthesis. The genome of T. princeps has a number of properties that distinguish it from the genomes of Buchnera aphidicola and Carsonella ruddii, the endosymbionts of aphids and psyllids, respectively. Among these properties are a high G+C content (57.1 mol%), the same G+C content in intergenic spaces and structural genes, and similar G+C contents of the genes encoding highly and poorly conserved proteins. The high G+C content has a substantial effect on protein composition; about one-third of the residues consist of four amino acids with high-G+C-content codons. Sequence analysis of DNA fragments containing the rRNA operon and adjacent regions from endosymbionts of several mealybug species suggested that there was a single duplication of the rRNA operon and the adjacent genes in an ancestor of the present T. princeps. Subsequently, in one mealybug lineage rpS15, one of the duplicated genes, was retained, while in another lineage it decayed. These results extend the diversity of the types of endosymbiotic associations found in plant sap-sucking insects.

Degenerative Minimalism in the Genome of a Psyllid Endosymbiont

Psyllids, like aphids, feed on plant phloem sap and are obligately associated with prokaryotic endosymbionts acquired through vertical transmission from an ancestral infection. We have sequenced 37 kb of DNA of the genome of Carsonella ruddii, the endosymbiont of psyllids, and found that it has a number of unusual properties revealing a more extreme case of degeneration than was previously reported from studies of eubacterial genomes, including that of the aphid endosymbiont Buchnera aphidicola. Among the unusual properties are an exceptionally low guanine-plus-cytosine content (19.9%), almost complete absence of intergenic spaces, operon fusion, and lack of the usual promoter sequences upstream of 16S rDNA. These features suggest the synthesis of long mRNAs and translational coupling. The most extreme instances of base compositional bias occur in the genes encoding proteins that have less highly conserved amino acid sequences; the guanine-plus-cytosine content of some protein-coding sequences is as low as 10%. The shift in base composition has a large effect on proteins: in polypeptides of C. ruddii, half of the residues consist of five amino acids with codons low in guanine plus cytosine. Furthermore, the proteins of C. ruddii are reduced in size, with an average of about 9% fewer amino acids than in homologous proteins of related bacteria. These observations suggest that the C. ruddii genome is not subject to constraints that limit the evolution of other known eubacteria.