Abstract
Background： Nicotiana tabacum is an important economic crop. Topping, a common agricultural practice employed with flue-cured tobacco, is designed to increase leaf nicotine contents. Many genes are found to be differentially expressed in response to topping, particularly genes involved in nicotine biosynthesis, but comprehensive analyses of early transcriptional responses induced by topping are not yet available. To develop a detailed understanding of the mechanisms regulating nicotine biosynthesis after topping, we have sequenced the transcriptomes of N. tabacum roots at seven time points following topping.
Results： Differential expression analysis revealed that 4,830 genes respond to topping across all time points. Amongst these, nine gene families involved in nicotine biosynthesis and two gene families involved in nicotine transport showed significant changes during the immediate 24 hour period following topping. No obvious preference to the parental species was detected in the differentially expressed genes (DEGs). Significant changes in transcript levels of nine genes involved in nicotine biosynthesis and phytohormone signal transduction were validated by qRT-PCR assays. 549 genes encoding transcription factors (TFs), found to exhibit significant changes in gene expression after topping, formed 15 clusters based on similarities of their transcript level time-course profiles. 336 DEGs involved in phytohormone signal transduction, including genes functionally related to the phytohormones jasmonic acid, abscisic acid, auxin, ethylene, and gibberellin, were identified at the earliest time point after topping.
Conclusions： Our research provides the first detailed analysis of the early transcriptional responses to topping in N. tabacum , and identifies excellent candidates for further detailed studies concerning the regulation of nicotine biosynthesis in tobacco roots.
Phenotypic characteristics of tobacco plants harboring mutations in nicotine biosynthesis genes from PMT and QPT gene families
