Molecular cloning of wheat dihydrodipicolinate synthase

Four forms of dihydrodipicolinate synthase (DHDPS), which catalyzes the first reaction in the lysine-specific biosynthetic pathway in higher plants, were purified to homogeneity from a suspension culture of wheat (Triticum aestivum). These polypeptides have similar N-terminal amino acid sequences. Two different cDNA clones were isolated by screening a wheat cDNA library with oligonucleotide probes based on these amino acid sequences. The predicted amino acid sequences indicate that both clones encode putative chloroplast transit peptides that have little homology to each other as well as the conserved mature protein portions of Mr 35,737 and 35,776 (94% identity). Mature wheat DHDPS has 30% amino acid identity to Escherichia coli DHDPS. One of the cloned cDNAs, which had been fused to bacterial transcription/translation signals, genetically complemented a strain of E. coli that lacks endogenous DHDPS activity. Moreover, the expression of wheat DHDPS cDNA in wild-type E. coli increased the enzymatic activity 10-fold in the transformed bacteria.