title: Plant phenolics are detoxified by prophenoloxidase in the insect gut.
abstract: Plant phenolics are a group of important secondary metabolites that are toxic to many animals and insects if ingested at high concentrations. Because most insects consume plant phenolics daily, they have likely evolved the capacity to detoxify these compounds. Here, we used Drosophila melanogaster, Bombyx mori and Helicoverpa armigera as models to study the metabolism of plant phenolics by prophenoloxidases. We found that insect foreguts release prophenoloxidases into the lumen, and that the survival of prophenoloxidase-deletion mutants was impaired when fed several plant phenolics and tea extracts. Using l-DOPA as a model substrate, biochemical assays in large Lepidopteran insects demonstrated that low levels of l-DOPA are rapidly metabolized into intermediates by phenoloxidases. Feeding with excess l-DOPA showed that the metabolic intermediate 5,6-dihydroxyindole reached the hindgut either by passing directly through the midgut, or by transport through the hemolymph. In the hindgut, 5,6-dihydroxyindole was further oxidized by prophenoloxidases. Intermediates exerted no toxicity in the hemocoel or midgut. These results show that plant phenolics are not toxic to insects unless prophenoloxidase genes are lost or the levels of phenolics exceed the catalytic activity of the gut prophenoloxidases.
authors.affiliation: Key Laboratory of Insect Developmental and Evolutionary Biology, Institute of Plant Physiology and Ecology, Shanghai Institutes for Biological Sciences, Chinese Academy of Sciences, Shanghai 200032, China.
authors.forename: Kai
authors.initials: K
authors.lastname: Wu
authors.affiliation: Key Laboratory of Insect Developmental and Evolutionary Biology, Institute of Plant Physiology and Ecology, Shanghai Institutes for Biological Sciences, Chinese Academy of Sciences, Shanghai 200032, China.
authors.forename: Jie
authors.initials: J
authors.lastname: Zhang
authors.affiliation: Key Laboratory of Insect Developmental and Evolutionary Biology, Institute of Plant Physiology and Ecology, Shanghai Institutes for Biological Sciences, Chinese Academy of Sciences, Shanghai 200032, China.
authors.forename: Qiaoli
authors.initials: Q
authors.lastname: Zhang
authors.affiliation: Key Laboratory of Insect Developmental and Evolutionary Biology, Institute of Plant Physiology and Ecology, Shanghai Institutes for Biological Sciences, Chinese Academy of Sciences, Shanghai 200032, China.
authors.forename: Shoulin
authors.initials: S
authors.lastname: Zhu
authors.affiliation: Key Laboratory of Insect Developmental and Evolutionary Biology, Institute of Plant Physiology and Ecology, Shanghai Institutes for Biological Sciences, Chinese Academy of Sciences, Shanghai 200032, China.
authors.forename: Qimiao
authors.initials: Q
authors.lastname: Shao
authors.affiliation: Department of Food Science and Technology, University of Georgia, Athens, GA 30602, USA.
authors.forename: Kevin D
authors.initials: KD
authors.lastname: Clark
authors.affiliation: Central Lab of Key Equipments, Institute of Plant Physiology and Ecology, Shanghai Institutes for Biological Sciences, Chinese Academy of Sciences, Shanghai 200032, China.
authors.forename: Yining
authors.initials: Y
authors.lastname: Liu
authors.affiliation: Key Laboratory of Insect Developmental and Evolutionary Biology, Institute of Plant Physiology and Ecology, Shanghai Institutes for Biological Sciences, Chinese Academy of Sciences, Shanghai 200032, China.
authors.forename: Erjun
authors.initials: E
authors.lastname: Ling
mesh_terms: D000818:Animals; D001711:Biotransformation; D012831:Bombyx / Q000201:enzymology* / Q000235:genetics / Q000378:metabolism; D004156:Catechol Oxidase / Q000172:deficiency / Q000235:genetics*; D004331:Drosophila melanogaster / Q000201:enzymology* / Q000235:genetics; D004792:Enzyme Precursors / Q000172:deficiency / Q000235:genetics*; D017353:Gene Deletion; D015870:Gene Expression; D006458:Hemolymph / Q000378:metabolism; D007211:Indoles / Q000378:metabolism; D019476:Insect Proteins / Q000172:deficiency / Q000235:genetics*; D007413:Intestinal Mucosa / Q000378:metabolism; D007915:Lepidoptera / Q000201:enzymology* / Q000235:genetics; D007980:Levodopa / Q000378:metabolism; D050216:Metabolic Detoxication, Phase I / Q000235:genetics*; D010636:Phenols / Q000378:metabolism*; D010936:Plant Extracts / Q000008:administration & dosage / Q000378:metabolism; D010944:Plants / Q000737:chemistry
chemical_list: D004792:Enzyme Precursors; D007211:Indoles; D019476:Insect Proteins; D010636:Phenols; D010936:Plant Extracts; D007980:Levodopa; C038451:pro-phenoloxidase; D004156:Catechol Oxidase; C033871:5,6-dihydroxyindole