RNAi strategies to induce gene silencing in the phytoplasma vector Euscelidius variegatus

The leafhopper Euscelidius variegatus is a natural vector of chrysanthemum yellows phytoplasma (CY) and an efficient vector of Flavescence dorée phytoplasma (FD) under laboratory conditions. Phytoplasmas are plant pathogenic bacteria transmitted by sap-feeding insects belonging to the order Hemiptera and associated with many diseases that cause severe economic impacts on many crops worldwide. In these study, gene silencing techniques mediated by RNA interference (RNAi) are applied to E. variegatus to shed light on insect genes potentially involved in the interaction with phytoplasmas, and, more specifically, in the acquisition and transmission mechanisms of these pathogens. In particular, the ability of actin and ATP synthase ? dsRNAs (double stranded RNAs) to induce RNAi effects after abdominalinjection is being tested. Both genes are known to be involved in the interaction between phytoplasmas and their insect hosts, so an efficient perturbation of their expression is likely to cause a modification in the epidemiological cycle of this plant disease. The possibility of using insect viruses as dsRNA delivery tools (or VIGS = virus induced gene silencing) is also explored. During a RNA-seq project of E. variegatus, a 10,616 nucleotide-long contig with high sequence similarity to known picorna-like viruses was in fact identified among the assembled insect transcripts. The synthesis of infectious clones of this virus, named Euscelidius variegatus virus 1 (EVV-1), would represent a groundbreaking tool to be used directly as biocontrol measures that interfere with the vector competence, providing additional tools to integrate or even replace insecticide treatments towards a more sustainable agriculture.