Soybean Kunitz, C-II and PI-IV inhibitor genes confer different levels of insect resistance to tobacco and potato transgenic plants

Abstract

In modern, highly intensive agriculture, the control of insect pests is basically achieved with the appli- cation of chemical pesticides. Heavy reliance on this sole strategy is associated with several drawbacks, and the de- velopment of alternative or complementary methods to chemical control is desirable. In this work, three soybean genes (KTi3, C-II and PI-IV) coding for serine proteinase inhibitors were isolated by PCR and transferred to Agro- bacterium tumefaciens EHA 105, which in turn was used for transforming tobacco leaf and potato tuber discs. Bio- chemical assays confirmed that transgenic plants synthe- sized serine proteinase inhibitors; rates of expression varied among plants. The level of insect resistance (tested with Spodoptera littoralis Boisduval) was particularly high in tobacco, where many plants caused the death of all larvae. In potatoes, larval mortality was much less fre- quently achieved, but the results were still encouraging in that larval weight gain was reduced by 50% in the pres- ence of adequate amounts of inhibitor. When 8-day-old larvae were fed different KTi 3 -expressing tobacco plants, a highly significant (P<0.01) correlation was observed be- tween inhibitor content and larval live weight. Larval weight gain was found to be dependent on midgut proteo- lytic activity. On the basis of the evidence collected, it is suggested that further work is required to identify more specific inhibitors for the main proteinases of the target in- sect.