title: Protein digestion in cereal aphids (Sitobion avenae) as a target for plant defence by endogenous proteinase inhibitors.
abstract: Gut extracts from cereal aphids (Sitobion avenae) showed significant levels of proteolytic activity, which was inhibited by reagents specific for cysteine proteases and chymotrypsin-like proteases. Gut tissue contained cDNAs encoding cathepsin B-like cysteine proteinases, similar to those identified in the closely related pea aphid (Acyrthosiphon pisum). Analysis of honeydew (liquid excreta) from cereal aphids fed on diet containing ovalbumin showed that digestion of ingested proteins occurred in vivo. Protein could partially substitute for free amino acids in diet, although it could not support complete development. Recombinant wheat proteinase inhibitors (PIs) fed in diet were antimetabolic to cereal aphids, even when normal levels of free amino acids were present. PIs inhibited proteolysis by aphid gut extracts in vitro, and digestion of protein fed to aphids in vivo. Wheat subtilisin/chymotrypsin inhibitor, which was found to inhibit serine and cysteine proteinases, was more effective in both inhibitory and antimetabolic activity than wheat cystatin, which inhibited cysteine proteases only. Digestion of ingested protein is unlikely to contribute significantly to nutritional requirements when aphids are feeding on phloem, and the antimetabolic activity of dietary proteinase inhibitors is suggested to result from effects on proteinases involved in degradation of endogenous proteins.
authors.affiliation: School of Biological and Biomedical Sciences, Durham University, South Road, Durham DH1 3LE, United Kingdom.
authors.forename: Prashant
authors.initials: P
authors.lastname: Pyati
authors.forename: Ali R
authors.initials: AR
authors.lastname: Bandani
authors.forename: Elaine
authors.initials: E
authors.lastname: Fitches
authors.forename: John A
authors.initials: JA
authors.lastname: Gatehouse
mesh_terms: D000818:Animals; D001042:Aphids / Q000201:enzymology* / Q000235:genetics / Q000378:metabolism; D002401:Cathepsin B / Q000235:genetics / Q000378:metabolism; D053818:Chymases / Q000235:genetics / Q000378:metabolism; D057056:Cysteine Proteases / Q000235:genetics / Q000378:metabolism; D018076:DNA, Complementary / Q000235:genetics / Q000378:metabolism; D004463:Ecology; D005260:Female; D041981:Gastrointestinal Tract / Q000201:enzymology; D019476:Insect Proteins / Q000235:genetics / Q000378:metabolism; D010047:Ovalbumin / Q000378:metabolism; D030821:Plants, Genetically Modified / Q000235:genetics / Q000378:metabolism; D011480:Protease Inhibitors / Q000378:metabolism; D057057:Serine Proteases / Q000235:genetics / Q000378:metabolism; D020860:Subtilisin / Q000235:genetics / Q000378:metabolism; D014908:Triticum / Q000737:chemistry* / Q000235:genetics / Q000502:physiology
chemical_list: D018076:DNA, Complementary; D019476:Insect Proteins; D011480:Protease Inhibitors; D010047:Ovalbumin; D057056:Cysteine Proteases; D057057:Serine Proteases; D053818:Chymases; D020860:Subtilisin; D002401:Cathepsin B