Transcriptomic analysis provides insights into the AUXIN RESPONSE FACTOR 6-mediated repression of nicotine biosynthesis in tobacco (Nicotiana tabacum L.)

Comparative transcriptome analysis reveals nicotine metabolism is a critical component for enhancing stress response intensity of innate immunity system in tobacco

The pyridine alkaloid nicotine acts as one of best-studied plant resistant traits in tobacco. Previous research has shown that NtERF199 and NtERF189, acting as master regulators within the NIC1 and NIC2 locus, quantitatively contribute to nicotine accumulation levels in N. tabacum. Genome editing-created Nic1(Nterf199) and Nic2 (Nterf189) double mutant provides an ideal platform for precisely dissecting the defensive role of nicotine and the connection between the nicotine biosynthetic pathway with other putative metabolic networks. Taking this advantage, we performed a comparative transcriptomic analysis to reevaluate the potential physiological and metabolic changes in response to nicotine synthesis defect by comparing the nic1nic2 and NIC1NIC2 plants. Our findings revealed that nicotine reduction could systematically diminishes the expression intensities of genes associated with stimulus perception, signal transduction and regulation, as well as secondary metabolic flux. Consequently, this global expression reduction might compromise tobacco adaptions to environmental fitness, herbivore resistances, and plant growth and development. The up-regulation of a novel set of stress-responsive and metabolic pathway genes might signify a newly established metabolic reprogramming to tradeoff the detrimental effect of nicotine loss. These results offer additional compelling evidence regarding nicotine's critical defensive role in nature and highlights the tight link between nicotine biosynthesis and gene expression levels of quantitative resistance-related genes for better environmental adaptation.

Genetic regulation and manipulation of nicotine biosynthesis in tobacco: strategies to eliminate addictive alkaloids

Tobacco (Nicotiana tabacum L.) is a widely cultivated crop of the genus Nicotiana. Due to the highly addictive nature of tobacco products, tobacco smoking remains the leading cause of preventable death and disease. There is therefore a critical need to develop tobacco varieties with reduced or non-addictive nicotine levels. Nicotine and related pyridine alkaloids biosynthesized in the roots of tobacco plants are transported to the leaves, where they are stored in vacuoles as a defense against predators. Jasmonate, a defense-related plant hormone, plays a crucial signaling role in activating transcriptional regulators that coordinate the expression of downstream metabolic and transport genes involved in nicotine production. In recent years, substantial progress has been made in molecular and genomics research, revealing many metabolic and regulatory genes involved in nicotine biosynthesis. These advances have enabled us to develop tobacco plants with low or ultra-low nicotine levels through various methodologies, such as mutational breeding, genetic engineering, and genome editing. We review the recent progress on genetic manipulation of nicotine production in tobacco, which serves as an excellent example of plant metabolic engineering with profound social implications.

Advances in regulatory mechanism(s) and biotechnological approaches to modulate nicotine content in tobacco

More than 8 million deaths are caused by tobacco-related diseases every year. A staggering 1.2 million of those fatalities occur due to second-hand smoke exposure among non-smokers, but more than 7 million are due to direct tobacco use among smokers. Nicotine acts as the key ingredient triggering the addiction. The United States Food and Drug Administration (FDA) has classified more than 90 chemical components of tobacco and related smoke as hazardous or potentially hazardous leading to cancer, cardiovascular, respiratory, and reproductive disorders. Hence, reducing nicotine content has been the foremost objective to reduce health and death risks. Therefore, various biotechnological approaches for developing tobacco varieties with low nicotine concentrations are urgently required for the welfare of humankind. In recent years, numerous advancements have been made in nicotine-based tobacco research, suggesting regulatory components involved in nicotine biosynthesis and developing nicotine-less tobacco varieties through biotechnological approaches. This review highlights the various regulatory components and major approaches used to modulate nicotine content in tobacco cultivars.