Aphids, which are important plant pests, adapt to seasonal periodism by developing alternative phenotypes. A viviparous asexual reproduction clonal process occurs in spring and summer and produces only parthenogenetic females, under long days. In the fall, when the photoperiod decreases, sexual morphs are produced, including oviparous sexual females. Eggs are laid before winter and a diapause allows a hatching in spring, when climatic conditions are again favorable. Deciphering the molecular processes of this phenotypic plasticity is still a challenge: photoperiodism is a biological switch that regulates most animal behaviors and plant life traits, in order to adapt to changing environment. Since 1970, it is known that in aphids, the photoperiodic signal is sensed by the pars intercerebralis, a specific area in the brain, but the molecule and the mechanisms associated with this sensing are still unknown. Several findings (anatomy, transcriptomic and genomic data) allow us to identify Insulin-Like Peptides (especially ILP-1 and ILP-5) as neurohormones that could be the candidates for this photoperiodic sensing in the pea aphid Acyrthosiphon pisum. The demonstration of this hypothesis would represent an important step in the knowledge of how this pest adapts to its environment through photoperiodic signals. This project aims at testing the hypothesis that ILPs are key elements in the triggering of the photoperiodic response for the reproductive mode plasticity. We plan to i) localize by immunocytochemistry and in situ hybridization the neurosecretory cells producing insulin, ii) track the axons of these cells of the pars intercerebralis by anterograde labelling (from the cellular body to the synapse), and 3) analyze the expression and regulation of the corresponding mRNAs in the brain of sexual and asexual females. These demonstrations could then be extended to functional analyses using CRISPR-Cas9 to check for the direct role of these ILPs in the phenotypic plasticity of the reproductive mode in aphids.
From Le Trionnaire et al. 2009 BMC Genomics 10:456
Figure 3 Nässel, Front Physiol 2013