ACCUMULATION OF A CHYMOTRYPSIN INHIBITOR IN TRANSGENIC TOBACCO CAN AFFECT THE GROWTH OF INSECT PESTS

A member of the potato proteinase inhibitor II (PPI II) gene family that encodes for a chymotrypsin iso-inhibitor has been introduced into tobacco (Nicotiana tabacum) using Agrobacterium tumefaciens-mediated T-DNA transfer. Analysis of the primary transgenic plants (designated R(0)) confirmed that the introduced gene is being expressed and the inhibitor accumulates as an intact and fully functional protein. For insect feeding trials, progeny from the self-fertilization of R(0) plants (designated R(1)) were used. Leaf tissue, either from transgenic or from control (non-transgenic) plants, was fed to larvae of Chrysodeixis eriosoma (Lepidoptera: Noctuidae, green looper), Spodoptera litura (F.) (Lepidoptera: Noctuidae) and Thysanoplusia orichalcea (F.) (Lepidoptera: Noctuidae) and insect weight gain (increase in fresh weight) measured. Consistently, C. eriosoma larvae fed leaf tissue from transgenic plants expressing the PPI II gene grew slower than insects fed leaf tissue from non-transgenic plants or transgenic plants with no detectable PPI II protein accumulation. However, larvae of both S. litura and T. orichalcea consistently demonstrated similar or faster growth when fed leaf tissue from transgenic plants compared with those fed non-transgenic plants. In agreement with the feeding trials, the chymotrypsin iso-inhibitor extracted from transgenic tobacco effectively retarded chymotrypsin-like activity measured in C. eriosoma digestive tract extracts, but not in extracts from S. litura. We conclude, therefore, that for certain insects the use of chymotrypsin inhibitors should now be evaluated as an effective strategy to provide field resistance against insect pests in transgenic plants, but further, that a single proteinase inhibitor gene may not be universally effective against a range of insect pests. The significance of these observations is discussed with respect to the inclusion of chymotrypsin inhibitors in the composite of insect pest resistance factors that have been proposed for introduction into crop plants.