Résumé : Aphids occupy a niche comprising two conceptual realms: a micron-scale feeding site beneath the plant surface, in which a syringe-like appendage mediates chemical exchange with a specific plant cell type and the larger realm of a metazoan with sensory organs, a nervous system, and behavior, all...Aphids occupy a niche comprising two conceptual realms: a micron-scale feeding site beneath the plant surface, in which a syringe-like appendage mediates chemical exchange with a specific plant cell type and the larger realm of a metazoan with sensory organs, a nervous system, and behavior, all responsive to the condition of the host plant and the broader environment. The biology that connects these realms is not well understood, but new details are emerging with the help of genomic tools. The power of these tools is set to increase substantially now that the first genome of an aphid is being sequenced and annotated. This has been possible because a community of aphid researchers focused their efforts to develop and share genomic resources through an international consortium. This complete genome sequence, along with other resources, should permit major advances in understanding the complex and peculiar biological traits responsible for aphids' evolutionary success and their damaging effects on agriculture. This review highlights early progress in the application of aphid genomics and identifies key issues of plant-aphid interactions likely to benefit as molecular tools are further developed. Use of this new knowledge could make significant contributions to crop protection against these and other phloem-feeding insects.
Résumé : Most aphids develop a cyclic parthenogenesis life-cycle. After several generations of viviparous parthenogenetic females, it follows a single annual generation of sexual individuals, usually in autumn, that mate and lay the sexual eggs. Shortening of photoperiod at the end of the summer is a key...Most aphids develop a cyclic parthenogenesis life-cycle. After several generations of viviparous parthenogenetic females, it follows a single annual generation of sexual individuals, usually in autumn, that mate and lay the sexual eggs. Shortening of photoperiod at the end of the summer is a key factor inducing the sexual response. With the survey here reported we aimed at identifying a collection of candidate genes to participate at some point in the cascade of events that lead to the sexual phenotypes. Following a suppression subtractive hybridization methodology (SSH) on the model aphid Acyrthosiphon pisum, we built and characterised two reciprocal cDNA libraries (SDU and SDD) enriched respectively in genes up-regulated or down-regulated by short photoperiod conditions that lead to the sexual response in this aphid species. A total of 557 ESTs were obtained altogether representing 223 non-overlapping contigs. 29% of these were new sequences not present in previous aphid EST libraries. BLAST searches allowed putative identification of about 54% of the contigs present in both libraries. Relative quantification of expression through real-time quantitative PCR demonstrated the differential expression in relation with the photoperiod of 6 genes (3 up-regulated and 3 down-regulated by shortening the day length). Among these, expression of a tubulin gene, two cuticular proteins and a yet unidentified sequence along the day-night cycle was further investigated. Implications for current studies on gene regulation of the dichotomy sex vs. parthenogenesis in aphids are discussed.