Mapping the Tobacco Genome to Help Reduce Nitrogen-based Fertilizers

British American Tobacco's plant growing chambers in Cambridge, U.K. Image credit: British American Tobacco

Researchers at the British American Tobacco Company have successfully identified and cloned two mutated genes of tobacco to discover how efficiently the plants use nitrogen.

The goal of the research is two-fold: To one day help reduce the need for nitrogen-based fertilizers in growing crops and to play a role in helping to reduce the levels of some carcinogenic compounds found in cigarette smoke.

Nitrogen-based fertilizers on crops can lead to excess nitrates in the environment, leading to water acidification and eutrophication as well as nutrients leaching from the soil. The result can cause reductions in both biodiversity and crop productivity, not to mention the impact on animal and human health.

In tobacco, these fertilizers can lead to high concentrations of some nitrogen-based compounds in the leaf, leading to tobacco-specific toxicants in smoke.

British American Tobacco worked with North Carolina State University and the Boyce Thompson Institute to develop a genetic roadmap of the tobacco genome, which is about 50 percent larger than a human genome. It is also more complicated than a human genome because it is allopolyploid—a hybrid of different ancestral species where each tobacco cell contains sets of chromosomes from the original species.

Because of these combined genomes, it is like trying to put together two jumbled jigsaw puzzles containing very similar but not identical pictures, researchers say.

“Generating this dramatically improved assembly for tobacco is a substantial step forward,” says Chris Proctor, chief scientific officer at British American Tobacco. “It will open up several avenues of research that will help scientists gain a greater understanding of the evolution of the tobacco plant to the identification of genes responsible for several traits, whether they be related to improving sustainability of agriculture, reducing the levels of toxicants in tobacco products, or improving the production of pharmaceuticals and biofuels.”

The discovery has already been used to explain why Burley tobacco is not very effective at utilizing nitrogen compared to other types of tobacco.

“Different cultivars of Burley tobacco all share these two gene mutations, giving us a handle on why they differ from other tobaccos,” says Allen Griffiths, head of plant biotechnology at British American Tobacco. “We believe this represents the first successful map-based gene discovery for N. tabacum, and demonstrates the value of a high-quality genome assembly for future research.”

Burley tobacco’s lower nitrogen use efficiency on its metabolism and growth shows that some plant variants contain increased levels of nicotine, other alkaloids and nitrites, resulting in higher levels of tobacco-specific nitrosamine (TSNA) compounds in the leaf. Modifying the mutant genes could potentially lead to the development of novel tobacco cultivars that contain low levels of TSNAs, researchers say.

The full research article can be found on the BMC Genomics web site.