Physiological adaptation explains the insensitivity of Baris coerulescens to transgenic oilseed rape expressing oryzacystatin I

• Published in: Insect biochemistry and molecular biology 1999-02, Vol.29 (2), p.131-138
• Main Authors: Bonadé-Bottino, Michel, Lerin, Jacques, Zaccomer, Bruno, Jouanin, Lise
• Format: Article
• Language: English
• Subjects: Baris coerulescens; Brassica napus; Brassica napus oleifera; Coleoptera; Curculionidae; Cysteine proteinase inhibitor; Insect resistance; Transgenic oilseed rape
• ISSN: 0965-1748; 1879-0240
• DOI: 10.1016/S0965-1748(98)00116-7

Larvae of Baris coerulescens Scop. (Coleoptera: Curculionidæ) exhibit a complex array of gut proteinase activities comprising cysteine and serine proteinases. The major cysteine proteinase activity, showing an optimum at pH 6.0, corresponds to at least 4 different proteinases. On the contrary, the minor serine proteinase activity, with an optimum at pH 9.0, seems to be due essentially to a single proteinase. The cysteine proteinase inhibitor oryzacystatin I (OC-I) inhibits completely the cysteine proteinase activity in vitro. However, larval growth and survival were not significantly different on control and transgenic oilseed rape plants expressing high levels of active OC-I. In larvae grown on transgenic plants, cysteine proteinase activity was dramatically decreased, whereas serine proteinase activity was increased by more than 2-fold, when compared to larvae raised on control plants. For both activities, no new proteinase was detected in insects fed plants expressing OC-I. These results suggest that partial compensation of the inhibition of cysteine proteinase activity by the increase in serine proteinase activity allowed the larvae to overcome the effects of OC-I consumption. This case illustrates problems that could arise when trying to achieve high levels of protection for plants against Coleopteran pests possessing a complex digestive proteinase pool.