AbstractAphids are major pests of most of the crops worldwide. Such a success is largely explained by the remarkable plasticity of their reproductive mode. They reproduce efficiently by parthenogenesis during spring and summer generating important damage on crops. At the end of the summer, asexual females perceive the photoperiod shortening and transduce this signal towards their embryos that change their reproductive fate to produce sexual individuals: males and oviparous females. After mating, those sexual oviparous females lay cold-resistant eggs. Previous studies based on large-scale transcriptomic analyses suggested that dopamine pathway might be a key player in the integration of decrease of the autumnal photoperiodic signal to promote the switch of embryonic germline fate. In this study, we investigated the role of dopamine pathway in the photoperiodic response of the pea aphid Acyrthosiphon pisum. We first analysed the level of expression of ten genes of this pathway in heads and embryos of aphids reared under long-days (asexual producers) or short-days (sexual producers). We then performed in situ hybridization experiments to localize in embryos the ddc and pale transcripts that are coding for two rate-limiting enzymes in dopamine synthesis. We then used pharmacological approaches to inject aphids with dopamine or a pale inhibitor to mimic short days and long days conditions and observe a putative effect on the distribution of their offspring. Altogether, our results indicate that photoperiod shortening is associated with a reduction in dopamine synthesis that might affect cuticle sclerotization process rather than neuro-transmission. Using CRISPR-Cas9 mutagenesis, we also tried to knock out ddc gene in eggs produced after the mating of sexual individuals. We could observe strong melanization defaults in ddc mutated eggs, which confidently mimicked drosophila phenotype. Nevertheless, such a lethal phenotype did not allow us to investigate the precise role of ddc in photoperiod shortening signal integration prior to the reproductive mode switch.
LARGE-SCALE CANDIDATE GENE SCAN REVEALS THE ROLE OF CHEMORECEPTOR GENES IN HOST PLANT SPECIALIZATION AND SPECIATION IN THE PEA APHID
