BBI and Kunitz serin-protease inhibitor action in tomato transgenic plants towards Helicoverpa armigera larvae

Abstract

Several crop varieties with agronomically-compatible levels of resistance to insects have been generated by Bt gene transfer. Plant proteinaceous proteinase inhibitors have potential for increasing resistance of crop to insect pests. Proteolytic activities in the larval guts of Helicoverpa armigera (a major pest of solanaceae) have been investigated and proved to be largely due to extracellular serine proteinases (trypsin- and chymotrypsin-like activities) with alkaline pH optimum. With the aim of obtaining tomato transgenic plants resistant to H. armigera larvae, we transformed - the cultivar Riogrande with the gene KTI3 (coding for a soybean Kunitz Inhibitor) and the cultivar UC-82 with the gene Pi-IV (coding for a soybean Bowman-Birk Inhibitor). Leaf extracts of transgenic plants contained significant levels of inhibitory activities towards both bovine pancreatic trypsin and insect trypsin-like enzyme, on average 187- and 5-fold higher-than controls, respectively. The trypsin inhibiting activity was found stable atdifferent plant phenological phases in fruits and leaves; this activity resulted stable for 24h in detached leaf discs used to feed insects. Both inhibiting activities were able to contrast development of H. armigera larvae, by interferring with midgut trypsin-like activity that was found higher in III-IV ages than other ages.