Existence of differential epigenetic control in a pair of cultivated tobacco (Nicotiana tabacum L.) cultivars harbouring contrast nicotine levels

Nicotine (NIC) is a primary and characteristic alkaloid in tobacco (Nicotiana sp.). To date, there have been no comprehensive studies conducted to assess the prevalence of epigenetic phenomena related to tobacco NIC levels. Therefore, our present research seeks to investigate the potential prevalence of two significant epigenetic markers, specifically chromatin organization and genomic DNA (gDNA) methylation, in relation to physiological levels of NIC in tobacco. Our agronomical-field studies on the cultivated tobacco (N. tabacum L.) germplasm collection screening revealed a contrast pair of tobacco cv., GP150 and GP98, that exhibit consistent differences in their inherent NIC levels. GP150 harbors inherently high-NIC levels in its green- [~1.27% d.w. (pre-topping) and 2.87% d.w. (post-topping)] and cured-leaves (~3.01% d.w.). On the contrary, GP98 harbors inherently low-NIC levels in its green- [~0.04% d.w. (pre-topping) and 0.07% d.w. (post-topping)] and cured-leaves (~0.09% d.w.). A comparative evaluation of epigenetics phenomenon revealed that GP150 and GP98 differ significantly in terms of: (1) chromatin organization, (2) gDNA methylation status, (3) gDNA 5-methylcytosine (5mC) levels and (4) gDNA methyltransferases activity. An induced physiological alteration in gDNA methylation corroborated with corresponding alterations in NIC level further substantiates an intriguing correlation between aforementioned epigenetics phenomenon(s) and NIC biosynthesis in tobacco. These results reinforce the need of future in-depth epigenetics studies on NIC biosynthesis and/ signalling pathways in tobacco.