Interference of Quinolinate Phosphoribosyltransferase Gene QPT Affects Agronomic Traits and Leaf Quality in Nicotiana tabacum L.

Quinolinate phosphoribosyltransferase (QPRTase), a key enzyme in ensuring nicotinic acid is available for the synthesis of defensive pyridine alkaloids in Nicotiana species, also plays an important role in nicotinamide adenine dinucleotide (NAD) biosynthesis. In this study, the morphological traits, the quality characteristics and photosynthetic parameters in QPT-overexpressing/interfering tobacco plants were investigated, respectively. Results showed that the interference of QPT gene not only reduced significantly the morphological traits including plant height, stem girth, leaf number and leaf length, etc. at 20 days after transplanting (DAT), but the flowering period was delayed 10-15 d in interfered tobaccos compared with the overexpressed, control and wild-type counterparts. However, at 40 DAT and 60 DAT, only three indexes (plant height, stem girth and leaf number) in QPT-interfering plants appeared significant difference in comparison with other three types of tobacco lines. Meanwhile, the determination results from nicotine, sugar, K⁺ and Cl^- content showed the nicotine content in interfered plants was always significantly lower than that in overexpressed plants, control and the wild-type ones respectively whatever toppling or not. At the same time, the toppling treatment also caused the increasement of K⁺ content among the four different tobacco lines, but the maximum increase amplitude of K⁺ content was found in QPT-overexpressing tobaccos while the minimum appeared in QPT-interfering plants. Finally, QPT-interference in transgenic tobaccos likewise affected the photosynthesis by reducing net photosynthetic rate (Pn), stomata conductance (Gs) and transpiration rate (Tr), while there was no significant difference between QPT-overexpressing plants and the controls and the wild-types.