Molecular cloning of cDNAs encoding a range of digestive enzymes from a phytophagous beetle, Phaedon cochleariae

To gain better knowledge of the variety of digestive enzymes in phytophagou s coleopteran pests, a sequencing screen of 76 random cDNAs from a gut libr ary from Phaedon cochleariae larvae was performed. The screen yielded 21 cD NAs encoding aminoacid sequences homologous to known digestive enzymes, mos t of them were cell wall-hydrolysing enzymes. The deduced protein sequences of 7 cDNAs encoding putative or-amylase, cysteine proteinase, trypsin, chy motrypsin, cellulase, pectinase and xylanase display all the structural fea tures that characterize these enzymes in other eukaryotic organisms. Except the a-amylase and chymotrypsin cDNAs, the other cDNAs probably derive from multigene families. The distribution of the corresponding enzymatic activi ties at various developmental stages of P. cochleariae was examined. a-amyl ase activity is present in guts of larvae and adults, proteinases are abund ant in guts of larvae and adults, but scarce in eggs and larval carcasses, xylanases are present in the guts of larvae and adults, as well as in carca sses of larvae, whereas cellulase and pectinase activities are distributed in larval and adult guts, larval carcasses, and eggs. Only a minor fraction of the cellulases is secreted by microorganisms, suggesting that P. cochle ariae synthesizes most of its own cell-wall hydrolysing enzymes. The physio logical role of the enzymes is discussed, as well as the significance of th ese results for pest management strategies involving transgenic plants expr essing enzyme inhibitors. (C) 1999 Elsevier Science Ltd. All rights reserve d.