Three nicotine demethylase genes mediate nornicotine biosynthesis in Nicotiana tabacum L.: functional characterization of the CYP82E10 gene.

In most tobacco (Nicotiana tabacum L.) plants, nornicotine is a relatively minor alkaloid, comprising about 2-5% of the total pyridine alkaloid pool in the mature leaf. Changes in gene expression at an unstable locus, however, can give rise to plants that produce high levels of nornicotine, specifically during leaf senescence and curing.

CYP82E4-mediated nicotine to nornicotine conversion in tobacco is regulated by a senescence-specific signaling pathway.

Nicotine to nornicotine conversion in tobacco (Nicotiana tabacum L.) is regulated by an unstable converter locus which in its activated state gives rise to a high nornicotine, low nicotine phenotype in the senescing leaves. In plants that carry the high nornicotine trait, nicotine conversion is primarily catalyzed by a cytochrome P450 protein, designated CYP82E4 whose transcription is strongly upregulated during leaf senescence.

Functional analysis of nicotine demethylase genes reveals insights into the evolution of modern tobacco.

Tobacco (Nicotiana tabacum L.) is a natural allotetraploid derived from the interspecific hybridization between ancestral Nicotiana sylvestris and Nicotiana tomentosiformis. The majority of cultivated tobacco differs from both of its progenitor species in that tobacco typically contains nicotine as the primary alkaloid, in contrast to its two progenitors that accumulate nornicotine in the senescing leaves.

Conversion of nicotine to nornicotine in Nicotiana tabacum is mediated by CYP82E4, a cytochrome P450 monooxygenase.

Nornicotine is a secondary tobacco alkaloid that is produced by the N-demethylation of nicotine. Nornicotine production and accumulation in tobacco are undesirable because nornicotine serves as the precursor in the synthesis of the well characterized carcinogen N'-nitrosonornicotine during the curing and processing of tobacco. Although nornicotine is typically a minor alkaloid in tobacco plants, in many tobacco populations a high percentage of individuals can be found that convert a substantial proportion of the nicotine to nornicotine during leaf senescence and curing.

Molecular characterization and functional analysis of the manganese-containing superoxide dismutase gene (sodA) from Streptococcus thermophilus AO54.

This report describes the isolation, sequencing, and functional analysis of the sodA gene, encoding Mn-superoxide dismutase, from Streptococcus thermophilus AO54. The gene was found to encode a 201 amino acid polypeptide with 88 and 83% identity to SodA from Streptococcus mutans and Streptococcus agalacticae, respectively. Primer extension analysis revealed a transcriptional start site 27 nucleotides upstream of initiation codon.