A spatial-temporal understanding of gene regulatory networks and NtARF-mediated regulation of potassium accumulation in tobacco.

After tobacco topping, changes in the auxin content could affect K uptake by inhibiting the activity of K uptake-related genes through the NtARF genes, thus causing changes in K content. Tobacco (Nicotiana tabacum) is a valuable industrial and commercial crop, and the leaf is its primary product. Topping (removing apical buds) is a common agronomic practice that significantly improves the yield of tobacco leaves. Potassium (K) plays an important physiological role in tobacco growth and leaf traits, including combustibility, aroma, and safety in cigarette products, and its levels are significantly decreased after topping. Here, to present global spatial-temporal gene expression profiles and gene regulatory networks of the core elements of K uptake, leaves and roots from topped and untopped plants at short- and long-term time points after topping were sampled for transcriptome analysis. We found that the wounding response was initiated in leaves in the early stages after topping. Then, in the long term, processes related to metabolism and transcription regulation, as well as ion binding and transport, were altered. The expression profiles showed that core elements of K uptake and xylem loading were drastically suppressed in roots after topping. Finally, transient expression experiments confirmed that changes in the auxin content could affect K uptake by inhibiting the activity of K uptake-related genes through the tobacco auxin response factor (NtARF) genes, thus causing changes in the K content. These results suggest that some ARFs could be selected as targets to enhance the expressions of K uptake transporters, leading to increment of K contents and improvement of leaf quality in tobacco breeding.