A salivary GMC oxidoreductase of Manduca sexta re-arranges the green leaf volatile profile of its host plant

Green leaf volatiles (GLVs) are short-chain oxylipins that are emitted from plants in response to stress. Previous studies have shown that oral secretions (OS) of the tobacco hornworm Manduca sexta , introduced into plant wounds during feeding, catalyze the re-arrangement of GLVs from Z -3- to E -2-isomers. This change in the volatile signal however is bittersweet for the insect as it can be used by their natural enemies, as a prey location cue. Here we show that (3 Z ):(2 E )-hexenal isomerase ( Hi-1 ) in M . sexta’s OS catalyzes the conversion of the GLV Z -3-hexenal to E -2-hexenal. Hi-1 mutants that were raised on a GLV-free diet showed developmental disorders, indicating that Hi-1 also metabolizes other substrates important for the insect’s development. Phylogenetic analysis placed Hi-1 within the GMCβ-subfamily and showed that Hi-1 homologs from other lepidopterans could catalyze similar reactions. Our results indicate that Hi-1 not only modulates the plant’s GLV-bouquet but also functions in insect development.