Insect resistance to sugar beet pests mediated by a Beta vulgaris proteinase inhibitor transgene.

Abstract

We transformed sugar beet (Beta vulgaris) hairy roots and Nicotiana benthamiana plants with a Beta vulgaris root gene (BvSTI) that codes for a serine proteinase inhibitor. BvSTI is a root gene cloned from the F1016 breeding line that has moderate levels of resistance to the sugar beet root maggot (Tetanops myopaeformis), a major pest of sugar beet. Root maggot damage deforms roots and predisposes them to other pests and pathogens that reduce yield and quality. Transformants had high levels of BvSTI or GUS gene expression driven by the constitutive 35S or the BvSTI gene specific promoter, respectively. Polyacrylamide gel electrophoresis zymograms revealed clear zones that corresponded to proteinase inhibitor (PI) activities at ~24, 26 and 28 kDa in the sugar beet BvSTI transformants and 26 and 28 kDa in the N. benthamiana plants. Several insect pests of sugar beet and tobacco were bioassayed for resistance on the BvSTI-transgenic plant materials. Spodoptera frugiperda (fall armyworm), Spodoptera exigua (beet armyworm) and Manduca sexta (tobacco hornworm) larvae that were fed tobacco leaves or sugar beet roots that express the BvSTI gene exhibited higher mortality rates or were delayed in growth and development relative to control larvae. Since serine proteases comprise the major digestive enzymes in root maggot midguts, our findings suggest that the BvSTI gene is likely involved in root maggot resistance mechanisms in the F1016 genotype.