Modulation of Polyamine Biosynthesis in Transformed Tobacco Plants by Targeting Ornithine Decarboxylase to an Atypical Subcellular Compartment

Ornithine decarboxylase (ODC) is a cytosolic enzyme that catalyses the direct decarboxylation of L-ornithine to putrescine, one of the rate-limiting steps of polyamine biosynthesis in plants. We targeted recombinant human ODC to the cytosol and apoplast of transformed tobacco (Nicotiana tabacum) plants, and evaluated the impact of subcellular compartmentalization on the accumulation of the enzyme and its corresponding metabolic product. Immunoblot analysis showed that human ODC accumulated to high levels in both the cytosol and apoplast of transiently transformed tobacco leaves. In stably transformed tobacco plants with ODC targeted to the apoplast, enzyme activity increased by up to 32fold (P < 0.001) and putrescine levels increased by up to 8.5-fold (P < 0.05) compared to wild type plants. These results demonstrate that the subcellular targeting of polyamine pathway enzymes may provide a useful strategy to enhance the accumulation and activity of enzymes involved in polyamine biosynthesis and may increase metabolic flux toward desired