Aphids are major pests of most of the crops worldwide. Such a success is largely explained by their remarkable ability to adapt to the fluctuations of their environment. They indeed display an extreme phenotypic plasticity (also called polyphenism), where one single genotype can produce alternative and discrete phenotypes better adapted to these fluctuations. They notably display during their annual life cycle a reproductive polyphenism that allow them to anticipate seasons. They indeed reproduce clonally (by parthenogenesis) during spring and summer thus colonizing rapidly agroecosystems and generating important damages through plant nutrients hijacking, toxin secretion or virus transmission. At autumn arrival, the photoperiod shortening signal is perceived in the heads of aphids and transduced towards their embryos that switch from a clonal to a sexual reproductive mode. The sexual individuals produced then mate to produce eggs that can overcome winter conditions in a diapausing state, before hatching in the next spring and establishing new clonal colonies. In nature, lineages that are able to switch from clonal to sexual reproduction (and termed as CP for cyclically parthenogenetic) coexist with lineages that have lost this ability (and termed as OP for obligatory parthenogenetic) and thus reproduce only clonally. Population genomics analyses on CP and OP populations from the pea aphid identified an 840-kb candidate genomic region controlling reproductive mode variation and containing 32 genes. This region thus harbors key regulator(s) of reproductive mode switch. Mutations within the coding or regulatory sequences affecting either protein function or gene expression levels of one or more of these candidate gene(s) are thus responsible for the OP phenotype. The AphiSwitch project thus aims at characterizing and functionally testing the role of the best candidate genes within this region to eventually identify the one(s) responsible for reproductive mode variation and thus being key regulators of the switch. To reach this objective, the project will involve three different complementary tasks, benefiting from the combination of functional genomics, bioinformatics and cell biology skills gathered by AphiSwitch consortium. The first task will aim at providing a complete list of the best candidate genes within the 32 genes form the genomic region thanks to a combination of sequencing, spatiotemporal characterization of their expression and cell biology approaches. The second task will consist in the creation for the best candidate genes of knocked-out lineages using the CRISPR-Cas9 targeted mutagenesis protocol. The mutant lineages will then be submitted to photoperiod shortening signal in order to identify the ones with a reproductive phenotype and thus prove the involvement of the corresponding gene in reproductive mode switch. The third task will be more technological since it will aim at completing the pea aphid functional toolbox by developing transgenesis and CRISPR-mediated Knock-In. These developments will be used for rescuing experiments of the mutants and thus providing definitive functional evidence of the role of the candidate genes in the process. The AphiSwitch project will eventually lead for the first time to the identification and functional validation of key regulator(s) of reproductive mode switch in aphids that might then potentially serve as specific target functions for more selective aphid management strategies thus contributing to more sustainable agriculture.

Partners: INRAE IGEPP and Collège de France