DIFFERENTIALLY REGULATED INHIBITOR-SENSITIVE AND INSENSITIVE PROTEASEGENES FROM THE PHYTOPHAGOUS INSECT PEST, HELICOVERPA-ARMIGARA, ARE MEMBERS OF COMPLEX MULTIGENE FAMILIES

Ingestion of soybean Kunitz trypsin inhibitor (SKTI) by larvae of the phytophagous insect pest Helicoverpa armigera induced production of in hibitor-insensitive protease activity, The induced activity was not du e to proteolytic enzymes of different mechanistic classes, but rather to variants of the existing enzymes, Characterization of cDNAs showed that sequences encoding proteins of the serine protease family were ab undant in gut tissue of both control and SKTI-fed insects. The majorit y of serine protease family cDNAs encode enzymes closely homologous to trypsin and chymotrypsin; comparison of these sequences shows variati on in amino acid residues within the region which would be in contact with a protein protease inhibitor, More diverged sequences which may n ot encode active proteases are also present. All the cDNAs examined we re found to derive from multigene families; at least 28 different gene s are present in the serine protease family. Chronic ingestion of SKTI results in some serine protease-encoding mRNA species increasing in l evel, whereas others decrease, Chymotrypsin-encoding mRNAs tend to inc rease in level as a result of SKTI ingestion, but no clear trend is sh own by trypsin-encoding mRNAs. It is suggested that multiple, varying protease-encoding genes are an adaptive mechanism for reducing the del eterious effects of plant protease inhibitors. (C) 1997 Elsevier Scien ce Ltd.