RESUMEN
BACKGROUND: The sequencing of the genome of the pea aphid Acyrthosiphon pisum revealed an unusual expansion of the miRNA machinery, with two argonaute-1, two dicer-1 and four pasha gene copies. In this report, we have undertaken a deeper evolutionary analysis of the phylogenetic timing of these gene duplications and of the associated selective pressures by sequencing the two copies of ago-1 and dcr-1 in different aphid species of the subfamily Aphidinae. We have also carried out an analysis of the expression of both copies of ago-1 and dcr-1 by semi-quantitative PCR in different morphs of the pea aphid life cycle. RESULTS: The analysis has shown that the duplication of ago-1 occurred in an ancestor of the subfamily Aphidinae while the duplication of dcr-1 appears to be more recent. Besides, it has confirmed a pattern of one conserved copy and one accelerated copy for both genes, and has revealed the action of positive selection on several regions of the fast-evolving ago-1b. On the other hand, the semi-quantitative PCR experiments have revealed a differential expression of these genes between the morphs of the parthenogenetic and the sexual phases of Acyrthosiphon pisum. CONCLUSIONS: The discovery of these gene duplications in the miRNA machinery of aphids opens new perspectives of research about the regulation of gene expression in these insects. Accelerated evolution, positive selection and differential expression affecting some of the copies of these genes suggests the possibility of a neofunctionalization of these duplicates, which might play a role in the display of the striking phenotypic plasticity of aphids.
Asunto(s)
Áfidos/genética , Duplicación de Gen , Perfilación de la Expresión Génica , Proteínas de Insectos/genética , MicroARNs/genética , Empalme Alternativo , Animales , Proteínas Argonautas/clasificación , Proteínas Argonautas/genética , Evolución Molecular , Femenino , Conversión Génica , Proteínas de Insectos/clasificación , Masculino , Modelos Genéticos , Datos de Secuencia Molecular , Filogenia , Reproducción/genética , Reacción en Cadena de la Polimerasa de Transcriptasa Inversa , Ribonucleasa III/clasificación , Ribonucleasa III/genética , Análisis de Secuencia de ADNRESUMEN
The first molecular studies on the phylogeny of aphids (Hemiptera: Aphididae) bumped into a striking lack of phylogenetic structure for taxa levels higher than tribe, probably as a consequence of the rapid adaptive radiation that this group of insects went through during the Late Cretaceous. Here we present a new attempt to infer the relationships between major aphid taxa by the separate and combined analysis of two nuclear sequences (the long-wavelength opsin gene and the elongation factor 1 alpha gene) and two mitochondrial sequences (the genes encoding the subunit 6 of the F-ATPase and the subunit II of the cytochrome oxidase). Our results confirm previous results with the grouping of the subfamilies analysed in three main lineages, that are named A+D (subfamilies Aphidinae, Calaphidinae, Chaitophorinae, Drepanosiphinae and Pterocommatinae), E+T (subfamilies Anoeciinae, Eriosomatinae, Hormaphidinae, Mindarinae and Thelaxinae) and L (subfamily Lachninae). Furthermore, phylogenetic reconstructions generally support the early branching of the subfamily Lachninae in the phylogeny of aphids. Although some relationships among subfamilies inside lineages are not highly supported, our results are compatible with a scenario for the evolution of aphid life cycles with only four transitions of feeding from gymnosperms to angiosperms and two origins of host alternation.
Asunto(s)
Áfidos/clasificación , Evolución Molecular , Factor 1 de Elongación Peptídica/genética , Filogenia , Opsinas de Bastones/genética , Animales , Áfidos/genética , Núcleo Celular/genética , ADN Mitocondrial/genética , Genes de Insecto , Modelos Genéticos , Análisis de Secuencia de ADNRESUMEN
Viviparous aphids (Aphididae) constitute a monophyletic group within the Homoptera with more than 4000 extant species worldwide but higher diversity in temperate regions. Several aspects of their biology account for attention paid to this group of insects. Their plant-sap-sucking way of feeding with many species transmitting viruses to crop plants has important implications on crop management strategies. Cyclical parthenogenesis associated in many groups to host alternation and elaborate polyphenisms is of special interests for evolutionists. Finally, the ancient association of most aphid species with intracellular endosymbiotic bacteria (Buchnera sp.) has also received much attention from evolutionists interested in mechanisms involved in the symbiotic process. Knowing the phylogenetic relationships among major aphid taxa is of special interest to evolutionists interested in the above issues. However, until recently, molecular approaches to aphid phylogeny were absent and discussions on the evolution of aphid life-cycles and on evolutionary aspects of their symbiotic association with Buchnera were framed by morphology-based phylogenies. Recently, two reports using molecular approaches attempted to address the yet unresolved phylogeny of Aphididae with limited although somehow different conclusions. In the present report we study the utility of the long-wave opsin gene in resolving phylogenetic relationships among seven subfamilies within the Aphididae. Our results corroborate some previously proposed relationships and suggest a revision of some others. In particular, our data support grouping the analysed aphid species into three main clades, being the subfamily Lachninae one of them, which contradicts its generally accepted sistership relationship with the subfamily Aphidinae. Moreover, our data also suggest a basal position of Lachninae which has implications on current discussions about the ancestrality of conifer-feeding in modern aphids.