Abstract
Although genetically modified (GM) plants expressing toxins from Bacillus thuringiensis (Bt) protect agricultural crops against lepidopteran and coleopteran pests, field-evolved resistance to Bt toxins has been reported for populations of several lepidopteran species. Moreover, some important agricultural pests, like phloem-feeding insects, are not susceptible to Bt crops. Complementary pest control strategies are therefore necessary to assure that the benefits provided by those insect-resistant transgenic plants are not compromised and to target those pests that are not susceptible. Experimental GM plants producing plant protease inhibitors have been shown to confer resistance against a wide range of agricultural pests. In this study we assessed the potential of AtSerpin1, a serpin from Arabidopsis thaliana (L). Heynh., for pest control. In vitro assays were conducted with a wide range of pests that rely mainly on either serine or cysteine proteases for digestion and also with three non-target organisms occurring in agricultural crops. AtSerpin1 inhibited proteases from all pest and non-target species assayed. Subsequently, the cotton leafworm Spodoptera littoralis Boisduval and the pea aphid Acyrthosiphon pisum (Harris) were fed on artificial diets containing AtSerpin1, and S. littoralis was also fed on transgenic Arabidopsis plants overproducing AtSerpin1. AtSerpin1 supplied in the artificial diet or by transgenic plants reduced the growth of S. littoralis larvae by 65% and 38%, respectively, relative to controls. Nymphs of A. pisum exposed to diets containing AtSerpin1 suffered high mortality levels (LC50 = 637 µg ml−1). The results indicate that AtSerpin1 is a good candidate for exploitation in pest control.
Highlights
Herbivorous pests of major crops are estimated to reduce yields by 8–15% worldwide [1]
The inhibition of trypsin- and chymotrypsin-like serine activities was investigated in extracts of the pests S. littoralis, S. nonagrioides, and T. molitor, and in extracts of the non-targets L. terrestris, B. terrestris, and C. carnea (Table 2)
The trypsin activities of the non-targets C. carnea larvae and B. terrestris were highly susceptible to AtSerpin1, with an inhibition of 70% and 90%, respectively, at the lowest concentration tested (0.15 mM)
Summary
Herbivorous pests of major crops are estimated to reduce yields by 8–15% worldwide [1]. Genetically modified (GM) plants expressing d-endotoxins from Bacillus thuringiensis (Bt) are providing significant control of agricultural insect pests and have reduced pesticide usage and production costs [2], [3]. Complementary pest control strategies are necessary both to assure that the benefits provided by insect-resistant transgenic plants are not compromised and to target those pests that are not susceptible to Bt toxins. GM crops producing plant serine or cysteine protease inhibitors have been shown to confer resistance against a wide range of agricultural pests [12]. Transgenic plants expressing protease inhibitors, rarely achieve the same level of pest control as transgenic plants expressing Bt toxins [13] because herbivores are able to use several strategies to adapt to the inhibitors [12]. The combination of two protease inhibitors can lead to adverse effects on the target species that are not obtained with either inhibitor alone [14]
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