[Cloning and expression of the key enzyme hyoscyamine 6 beta-hydroxylase gene (DaH6H) in scopolamine biosynthesis of Datura arborea].

Hyoscyamine 6 beta-hydroxylase (H6H) is the last rate-limiting enzyme directly catalyzing the formation of scopolamine in tropane alkaloids (TAs) biosynthesis pathway. It is the primary target gene in the genetic modification of TAs metabolic pathway. Full-length cDNA and gDNA sequences of a novel H6H gene were cloned from Datura arborea (DaH6H, GenBank accession numbers for cDNA and gDNA are KR006981 and KR006983, respectively). Nucleotide sequence analysis reveals an open reading frame of 1375 bp encoding 347 amino acids in the cDNA of DaH6H, while the gDNA of DaH6H contains four exons and three introns, with the highest similarity to the gDNA of H6H from D. stramonium. DaH6H also exhibited the most identity of 90.5% with DsH6H in amino acids and harbored conserved 2-oxoglutarate binding motif and two iron binding motifs. The expression level of DaH6H was highest in the mature leaf, followed by the secondary root, and with no expression in the primary root based on qPCR analysis. Its expression was inhibited by MeJA. DaH6H was expressed in E. coli and a 39 kD recombinant protein was detected in SDS-PAGE. Comparison of the contents of scopolamine and hyoscyamine in various TAs-producing plants revealed that D. arborea was one of the rare scopolamine predominant plants. Cloning of DaH6H gene will allow more research in the molecular regulatory mechanism of TAs biosynthesis in distinct plants and provide a new candidate gene for scopolamine metabolic engineering.