Polyploidization Redirects Carbon Flux to Diterpenoid Biosynthesis in Nicotiana sylvestris

Polyploidization frequently rewires plant metabolism, leading to increased biomass and altered metabolic profiles. This makes it a promising strategy for crop improvement and breeding. However, the mechanism underlying this metabolic reprogramming remains largely unknown. In this study, we generated three stable autotetraploid Nicotiana sylvestris lines through colchicine treatment of diploids followed by continuous selection. Comparative metabolomic and transcriptomic analysis revealed 467 and 167 differential accumulated metabolites, as well as 587 and 154 differentially expressed genes between tetraploids and diploids in leaves and flowers, respectively. The increased expression levels of Calvin–Benson cycle genes and the elevated contents of pyruvate and glyceraldehyde-3-phosphate indicated enhanced photosynthetic carbon assimilation in tetraploid plants. Notably, the amounts of diterpenoids, such as cembratrienediol (CBT-diol) and cis-abienol, increased dramatically in tetraploids, whereas sucrose, the major product of photosynthesis, was markedly depleted. Consistent with this, the expression levels of the methylerythritol phosphate pathway and diterpene biosynthesis genes were upregulated, while sucrose phosphate synthase was downregulated in autotetraploid plants. These results suggest that polyploidization enhanced carbon assimilation and redirects the increased metabolic flux towards diterpenoid biosynthesis, rather than carbohydrate metabolism. Our findings provide new insight into the metabolic switch orchestrated by polyploidization, establish a mechanistic framework for polyploidy-driven metabolic innovation, and highlight autopolyploidization as a promising strategy for metabolic engineering and crop improvement.