NtPHT2;1 promotes tobacco growth by integrating chloroplast phosphate utilization with photosynthesis and carbon-nitrogen metabolism.

Phosphorus (P) is an essential macronutrient required for plant growth and productivity, and its uptake and distribution are mediated by members of the phosphate transporter (PHT) family. Among them, the transporter PHT2.1 has been implicated in chloroplast phosphate homeostasis; however, its role in coordinating plant growth and primary metabolism remains insufficiently defined. In this study, we cloned a phosphate transporter gene from Nicotiana tabacum L., designated NtPHT2;1. The gene is predominantly expressed in leaves, and its transcript level slightly decreases under low-phosphate conditions. Subcellular localization demonstrated that NtPHT2;1 resides in the chloroplasts. Genetic analyses revealed that overexpression of NtPHT2;1 increased leaf inorganic phosphate content by approximately 20% and significantly raised chlorophyll content under both sufficient and low phosphorus conditions, leading to enhanced photosynthetic capacity and a 10-15% increase in total biomass accumulation. In contrast, knockout plants exhibited reduced photosynthetic performance and impaired growth. Physiological and biochemical analyses further showed that NtPHT2;1 overexpression elevated the sucrose-to-starch ratio and increased nitrate (NO₃⁻) content by 15%, alongside enhanced nitrogen assimilation, indicating improved coordination between carbon and nitrogen metabolism. Field evaluations confirmed that overexpression lines displayed increased plant height, leaf area, and thousand-grain weight compared with wild-type plants. Collectively, these findings demonstrate that NtPHT2;1 contributes to internal phosphate utilization and is associated with coordinated regulation of photosynthesis and carbon-nitrogen metabolism, thereby promoting plant growth and yield potential. This work expands the functional understanding of the PHT2.1 subfamily and highlights chloroplast phosphate utilization as a promising target for improving phosphorus use efficiency in crops.