Ionotropic receptors participate in the perception of sinigrin in Plutella xylostella adults

Glucosinolates serve as the key gustatory cue for crucifer specialists to select their host plants, however, the molecular mechanisms underlying the gustation remain poorly understood. Here, we demonstrated that two ionotropic receptor co-receptors (Ircos) were involved in the perception of a major glucosinolate, sinigrin, in the adult Plutella xylostella. First, we cloned 13 gustatory receptors (GRs) expressed in adults (antennae and tarsi) and larvae (heads), and analyzed their functions using the Xenopus oocyte expression system. It showed that none of these GRs responded to sinigrin. Then we turned to ionotropic receptors (IRs), particularly the two Ircos (PxylIR25a and PxylIR76b), starting with establishment of two single Irco knockout and one double Ircos knockout insect strains using CRISPR-Cas9 approach. Further behavioral assays revealed that knockout of these two Ircos (in both single and double knockout) significantly reduced the sinigrin perception in female adults with no difference among the three knockout strains, suggesting that the two IRs participate in collaboration in the sinigrin perception. However, larval feeding preference for the sinigrin remained generally unaffected in the three knockout strains. These results demonstrate that adult P. xylostella perceive sinigrin at least partly through IR-mediated pathway, but the larvae employ other pathways. Our findings provide new insights into the gustatory mechanisms of glucosinolates, and provide potential molecular targets for development of new control strategies in P. xylostella and other crucifer specialists.