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.

FIG. 1.

Agarose gel electrophoresis of 16S-23S rDNA PCR products amplified from total DNA of three species of whiteflies. Lanes 1 and 11, molecular size standards; UD, undigested DNA; ClaI and SalI, restriction enzymes; Bta, B. tabaci; Nan, N. andropogonis; Aac, A. aceris. Bands of 0.1 kb (lanes 5, 6, and 7) and 0.2 kb (lanes 5 and 6) are not visible in the photograph.

FIG. 2.

Phylogenetic relationships of representative P-endosymbionts of plant sap-sucking insects, other insect P-endosymbionts, and related free-living bacteria. Trees are from maximum-likelihood analyses of the combined 16S-23S rDNAs. Numbers at nodes are for bootstrap percentages from 500 replicates; only nodes supported by 70% or greater are shown. P-endosymbionts that are designated by genus and species names in regular letters have “Candidatus” status. Italicized P-endosymbiont genus and species names were named prior to the “Candidatus” proposal; hence, they bear the usual species designations. Names within brackets refer to insect species from which the endosymbiont 16S-23S rDNA sequence was determined; other names refer to bacterial species. Greek letters by brackets indicate the subdivisions of the Proteobacteria. %G+C indicates the moles percent guanine-plus-cytosine content of either fragments of P-endosymbiont DNA or the whole genome (aphids). GenBank accession numbers are given in this paper or in references and 36).

FIG. 3.

Phylogenetic tree from maximum-likelihood analyses of whitefly P-endosymbiont-combined 16S-23S rDNA nucleotide sequences (A) and host mitochondrial combined cytB-nd1-LrDNA (B). Designations refer to whitefly species. In panel B, vertical striped lines are used to join organisms within the same genus. Filled diamonds in panel B indicate nodes identical to those in panel A, filled squares indicate consistent nodes, an open square indicates an inconsistent node, striped vertical lines indicate species within the same genus, thick double-headed arrows indicate major clusters, and thin double-headed arrows indicate species in different subfamilies. Numbers at nodes are for bootstrap percentages from 500 replicates; only nodes supported by 70% or greater are shown.