Overexpression of glutamate decarboxylase in transgenic tobacco plants deters feeding by phytophagous insect larvae

Gamma-aminobutyrate (GABA) is a ubiquitous four-carbon, nonprotein amino acid synthesized by glutamate decarboxylase. Previous research suggests that the endogenous synthesis of GABA, a naturally occurring inhibitory neurotransmitter at neuromuscular junctions, serves as a plant resistance mechanism against invertebrate pests. In this study, two homozygous transgenic tobacco lines constitutively overexpressing a single copy of a full-length chimeric glutamate decarboxylase cDNA and possessing enhanced capacity for GABA accumulation (GAD plants), a homozygous transgenic line lacking the gene insert, and wild-type tobacco were employed. Tobacco budworm larvae were presented with plantattached wild type and transgenic leaves for 4 hr in a feeding preference study. Larvae consumed six to twelve times more leaf tissue from wild-type plants than from GAD plants. These results suggest that leaf GABA accumulation, which is known to occur in response to insect larval walking and feeding, represents a rapidly deployed localresistance mechanism.