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Effect of day-length shortening on gene expression on pea aphid heads

ABSTRACT: Seasonal photoperiodism is responsable in aphid for the switch from asexual to sexual reproduction. In order to identify genes regulating the photoperiodic response, a cDNA microarray from the pea aphid was used to compare RNA populations from short- and long-day reared aphids. Analyses revealed that 64 different transcripts were significantly regulated, with a strong biological signature for cuticular proteins and proteins involved in cellular signalling or signal transduction. Quantitative PCR experiments performed on 5 transcripts confirmed microarray results. Complementary experiments eliminated moulting and circadian rhythms as putative confounding effects. Keywords: Stress response, Environmental cue

ORGANISM(S): Acyrthosiphon pisum

PROVIDER: GSE6363 | GEO | 2006/11/28

SECONDARY ACCESSION(S): PRJNA99577

REPOSITORIES: GEO

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Project description:Background: The best studied insect-symbiont system is that of aphids and their primary bacterial endosymbiont Buchnera aphidicola. Buchnera inhabits specialized host cells called bacteriocytes, provides nutrients to the aphid and has co-speciated with its aphid hosts for the past 150 million years. We have used a single microarray to examine gene expression in the pea aphid, Acyrthosiphon pisum, and its resident Buchnera. Very little is known of gene expression in aphids, few studies have examined gene expression in Buchnera, and no study has examined simultaneously the expression profiles of a host and its symbiont. Expression profiling of aphids, in studies such as this, will be critical for assigning newly discovered A. pisum genes to functional roles. In particular, because aphids possess many genes that are absent from Drosophila and other holometabolous insect taxa, aphid genome annotation efforts cannot rely entirely on homology to the best-studied insect systems. Development of this dual-genome array represents a first attempt to characterize gene expression in this emerging model system. Results: We chose to examine heat shock response because it has been well characterized both in Buchnera and in other insect species. Our results from the Buchnera of A. pisum show responses for the same gene set as an earlier study of heat shock response in Buchnera for the host aphid Schizaphis graminum. Additionally, analyses of aphid transcripts showed the expected response for homologs of known heat shock genes as well as responses for several genes with unknown functional roles. Conclusions: We examined gene expression under heat shock of an insect and its bacterial symbiont in a single assay using a dual-genome microarray. Further, our results indicate that microarrays are a useful tool for inferring functional roles of genes in A. pisum and other insects and suggest that the pea aphid genome may contain many gene paralogs that are differentially regulated. Keywords: Stress response

Project description:Aphid adaptation to harsh winter conditions is illustrated by an alternation of their reproductive mode. Aphids detect photoperiod shortening by sensing the length of the night and switch from viviparous parthenogenesis in spring and summer, to oviparous sexual reproduction in autumn. The photoperiodic signal is transduced from the head to the reproductive tract to change the fate of the future oocytes from mitotic diploid embryogenesis to haploid formation of gametes. Because of viviparous parthenogenesis, the whole process takes place in three consecutive generations. To understand the molecular basis of the switch in the reproductive mode, a transcriptomic approach was used to detect significantly regulated transcripts in the heads of the pea aphid Acyrthosiphon pisum. The transcriptomic profiles of the heads of the first generation were slightly affected by photoperiod shortening. This suggests that trans-generation signaling does not occur between the grand-mothers and the viviparous embryos they contain. By analogy, many of the genes regulated in the heads of the second generation are implicated in visual functions, photoreception and cuticle structure. The modification of the cuticle could decrease the storage of N-Î²-alanyldopamine and provoke an increase in free dopamine concentration. Based in results in Drosophila, modification of the insulin pathway could cause a decrease of juvenile hormones in short-day reared aphids. Biological material for microarray experiments was prepared under two dayly photoperiodic regimes both at constant temperature of 18Â°C: i) âShort Nightâ (SN) at 16h of light and ii) âLong Nightâ (LN) at 12h of light to induce the production of sexual morphs. To initiate the experiment, two groups of 105 L3 larvae were placed either under SN or LN condition. This corresponds to generation G0. At the middle of the photophase, 25 individual were frozen when they had reached both the L4 and the wingless adult (WA) stages, in the two photoperiod conditions. The 55 remaining WA individuals (still divided in two groups) were left on 55 plants to lay their offspring: one larva of the 1st stage (L1) was kept per WA. This larva was selected among the 20 first born larvae. This is the generation G1. At the middle of the photophase, 25 individual were frozen when they had reached both the L2 and the L4 stages, in the two photoperiodic conditions. Thus, 25 individuals from 4 different stages (L4-G0, WA-G0, L2-G1 and L4-G1) were collected in the two photoperiod conditions with 3 biological replicates, forming the 24 samples used for microarray experiments. RNAs from heads of aphids from the two photoperiodic conditions were hybridized one against the other for each stage with a dye-swap.The experimental design is thus 24 arrays which corresponds to the described samples of that series.

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Effect of day-length shortening on gene expression on pea aphid heads

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