Impact of nicotine pathway downregulation on polyamine biosynthesis and leaf ripening in tobacco.

Traditional breeding and molecular approaches have been used to develop tobacco varieties with reduced nicotine and secondary alkaloid levels. However, available low-alkaloid tobacco varieties have impaired leaf quality likely due to the metabolic consequences of nicotine biosynthesis downregulation. Recently, we found evidence that the unbalanced crosstalk between nicotine and polyamine pathways is involved in impaired leaf ripening of a low-alkaloid (LA) Burley 21 line having a mutation at the and loci, key biosynthetic regulators of nicotine biosynthesis.

Genetic attenuation of alkaloids and nicotine content in tobacco (Nicotiana tabacum).

The role of six alkaloid biosynthesis genes in the process of nicotine accumulation in tobacco was investigated. Downregulation of ornithine decarboxylase, arginine decarboxylase, and aspartate oxidase resulted in viable plants with a significantly lower nicotine content. Attenuation of nicotine accumulation in Nicotiana tabacum was addressed upon the application of RNAi technologies.

Polyamines delay leaf maturation in low-alkaloid tobacco varieties.

The development of low-alkaloid (LA) tobacco varieties is an important target in the tobacco breeding industry. However, LA Burley 21 plants, in which the and loci controlling nicotine biosynthesis are deleted, are characterized by impaired leaf maturation that leads to poor leaf quality before and after curing. Polyamines are involved in key developmental, physiological, and metabolic processes in plants, and act as anti-senescence and anti-ripening regulators.

Downregulation of the CpSRP43 gene expression confers a truncated light-harvesting antenna (TLA) and enhances biomass and leaf-to-stem ratio in Nicotiana tabacum canopies.

Downregulation in the expression of the signal recognition particle 43 (SRP43) gene in tobacco conferred a truncated photosynthetic light-harvesting antenna (TLA property), and resulted in plants with a greater leaf-to-stem ratio, improved photosynthetic productivity and canopy biomass accumulation under high-density cultivation conditions. Evolution of sizable arrays of light-harvesting antennae in all photosynthetic systems confers a survival advantage for the organism in the wild, where sunlight is often the growth-limiting factor. In crop monocultures, however, this property is strongly counterproductive, when growth takes place under direct and excess sunlight.