Tobacco Plants Transformed with the Bean Alphaai Gene Express an Inhibitor of Insect Alpha-Amylase in Their Seeds

Bean (Phaseolus vulgaris L.) seeds contain a putative plant defense protein that inhibits insect and mammalian but not plant alpha-amylases. We recently (J Moreno, MJ Chrispeels [1989] Proc Natl Acad Sci USA 86:7885-7889) presented strong circumstantial evidence that this alpha-amylase inhibitor (alphaAI) is encoded by an already-identified lectin gene whose product is referred to as lectin-like-protein (LLP). We have now made a chimeric gene consisting of the coding sequence of the lectin gene that encodes LLP and the 5' and 3' flanking sequences of the lectin gene that encodes phytohemagglutinin-L. When this chimeric gene was expressed in transgenic tobacco (Nicotiana tabacum), we observed in the seeds a series of polypeptides (M(r) 10,000-18,000) that cross-react with antibodies to the bean alpha-amylase inhibitor. Most of these polypeptides bind to a pig pancreas alpha-amylase affinity column. An extract of the seeds of the transformed tobacco plants inhibits pig pancreas alpha-amylase activity as well as the alpha-amylase present in the midgut of Tenebrio molitor. We suggest that introduction of this lectin gene (to be called alphaai) into other leguminous plants may be a strategy to protect the seeds from the seed-eating larvae of Coleoptera.