A new study published in BMC Genomics suggests the possibility of ‘less toxic’ cigarettes in future as scientists have managed to identify and clone two mutated genes associated with how efficiently tobacco plants used nitrogen and these same genes could also play a role in helping to reduce the levels of some carcinogenic compounds in cigarette smoke.
Nitrogen based fertilizers help us boost yield, but they have major negative effects on environment as well. Excess of nitrate in the environment can lead to water acidification and eutrophication with nutrients leaching from the soil. This can cause reductions in biodiversity and crop productivity, as well as having negative impacts on both animal and human health.
In the case of tobacco, inefficient metabolism of nitrogen by the plant can lead to high concentrations of some nitrogen-based compounds in the leaf, the presence of which lead to the formation of certain tobacco-specific toxicants in smoke.
Scientists have developed a new genetic roadmap of the tobacco genome (Nicotiana tabacum) that lays out the position of (or “anchors”) 64% of the tobacco genome, compared to just 20% in previous attempts.
The new assembly has already been used to successfully identify two mutated genes that explain why Burley tobacco is not very effective at utilizing nitrogen compared with other types of tobacco.
Nitrogen is essential for plant growth, and many farmers add nitrogen-based fertilizers to crops to achieve good yields. However, excess nitrogen can have adverse effects on the environment. The discovery of these genes could, therefore, help improve the nitrogen use efficiency of some types of tobacco, as well as other commercially important crops — ultimately reducing the need for chemical fertilizers
The impact of Burley’s lower nitrogen use efficiency on its metabolism and growth means that some plant variants contain increased levels of nicotine, other alkaloids, and nitrites, resulting in higher levels of tobacco-specific nitrosamine (TSNA) compounds in their leaf. Modifying the mutant genes could potentially also lead to the development of novel tobacco cultivars that contain lower levels of TSNAs.
To anchor the genetic code, the researchers used a new technique known as optical mapping. This involves taking a fingerprint of the genome — marking specific sequence patterns in very long sequences of unknown DNA — to create a barcode of DNA fragments. The barcode is then used as a template onto which the new assembly can be dropped and matched, a bit like completing a jigsaw on top of a trace of its picture. This has enabled much more of the genome to be anchored to tobacco chromosomes compared to previous assemblies.