[OsSTP1 mediates sucrose allocation to regulate rice responses to different nitrogen supply levels]

Improving the nitrogen use efficiency is an effective way to increase the yield of rice, and maintaining carbon-nitrogen balance is essential for the normal growth and development of rice. To investigate the impact of the sucrose transporter protein OsSTP1 on nitrogen absorption in rice, in this study, we constructed transgenic lines overexpressing the sucrose transporter gene OsSTP1 (OsSTP1-OE1, OsSTP1-OE2) and mutant transgenic lines (osstp1-1, osstp1-2) from the wild type TB309. Further, we conducted a hydroponic experiment with four nitrogen supply levels of free nitrogen (FN, 0 mg/L), low nitrogen (LN, 10 mg/L), normal nitrogen (NN, 40 mg/L), and high nitrogen (HN, 80 mg/L) to study the responses of each line to different nitrogen supply levels during the seedling stage. The results showed that compared with the wild type and mutant lines in the LN group, the OsSTP1-overexpressing lines exhibited significantly increased biomass, root length, and plant height, decreased soluble sugar content in the leaves, and increased soluble sugar content in the roots. The results indicate that the soluble sugars produced by leaf photosynthesis are transported to the roots through the phloem to promote root growth and nitrogen uptake, thus increasing the aboveground biomass. This study has identified that OsSTP1 can affect the long-distance transport of carbohydrates from source to sink to promote root growth, ultimately influencing rice's absorption and accumulation of nitrogen, improving nitrogen use efficiency and providing reference for reducing nitrogen fertilizer application.