Abstract: A novel holotype cry gene (cry1Dd1) was cloned from a Bt strain BN23-5, which enriches novel lepidopteran insecticidal Bt genes. In this study, the full length of the cry1Dd1 gene was cloned. The full-length cry1D gene was 3501 bp, encoding a polypeptide of 1166 amino acid residues. Its amino acid sequence was 86% identical to that of Cry1Db1, and the gene was named as cry1Dd1 by International Nomenclature Commitee of B. thuringiensis endotoxin with a GenBank number of KJ728844. The cry1Dd1 gene was inserted into a shuttle vector (pSTK) and expressed in an acrystalliferous mutant B. thuringiensis HD73^-. In this transformant, cry1Dd1 was expressed and diamond-shaped parasporal crystals were formed. SDS-PAGE analysis determined a molecular mass of approximately 130 kD of Cry1Dd1 protein. The Cry1Dd1 protein exhibited high larvicidal activity against the diamondback moth (Plutella xylostella), with an LC₅₀ of 13.1 μg/mL, and obviously inhibited growth of Spodoptera exigua larvae, but showed no insecticidal activity against Helicoverpa armigera larvae. Sequence analysis of the gene indicated that the cry1Dd1 gene retained eight conserved regions commonly found in the existing cry genes, and the function domain of Cry1Dd1 protein was the 37 to 593 amino acid residues at the N-terminal.

Key words: Bacillus thuringiensis, cry1Dd1 gene, Plutella xylostella, novel gene, parasporal crystal