Background:
Sucrose phosphate phosphatase (SPP) and uridine diphosphate-glucose pyrophosphorylase (UGPase) genes were overexpressed in Nicotiana tabacum to enhance the efficiency of the photosynthesis-related sucrose synthesis pathway, the primary route for incorporating newly fixed carbon into plant metabolism.

Material and methods:
To target transgene expression specifically to the leaves, the Chrysanthemum x morifolium Rubisco small subunit promoter was used.

Results:
Transgenic plants overexpressing HvSPP and HvUGPase exhibited high transgene expression in the leaves, exceeding those of the corresponding N. tabacum genes by more than tenfold. These plants grew faster and entered the generative phase earlier than control plants, without showing any other developmental abnormalities. By the end of the generative phase, transgenic plants had greater dry mass and contained a higher proportion of carbohydrates than the control group. In result, they accumulated 14.9–17.5% more energy in the aboveground parts compared to reference plants.

Conclusions:
The high leaf specificity of the C. x morifolium Rubisco small subunit promoter was confirmed, indicating that transgene activity in leaves was effectively separated from its effects on metabolism in non-photosynthetic tissues. Overexpression of HvUGPase and HvSPP under this promoter accelerated plant growth and development, ultimately increasing biomass. These characteristics are particularly advantageous for energy crops grown as after-crops or in regions with short growing seasons.