Isolation and Characterization of a Serine Proteinase Inhibitor cDNA from Cabbage and its Antibiosis in Transgenic Tobacco Plants

Plant proteinase inhibitors (PIs) are of special interest because of their role in plant defense against herbivorous insects. We isolated a cDNA clone for a serine PI from Brassica oleracea, cabbage (BoPI). A comparison of the putative coding sequence from the cabbage clone with soybean trypsin inhibitor identified conserved amino acids and peptide motifs. Furthermore, it seems to be a member of a 6-8 gene family in cabbage. The serine PI cDNA was subcloned into a plant expression vector under the control of the CaMV 35S promoter, and transgenic Nicotiana tabacum (tobacco) cv Xanthi were produced to test the ability of BoPI to enhance resistance against insects in a heterologous system. These plants were compared with transgenic plants containing different insect resistance transgenes (proteinase inhibitors and a Bacillus thuringiensis cry1Ac). The transgenic plants containing BoPI gene outperformed over other transgenic plants produced with diffierent PI genes, and compared favorably with Bt cry1Ac transgenic plants in a bioassay with Heliothis virescens, tobacco budworm.