Mutation of Ugp1 Leads to Impaired Sucrose Synthesis, Retarded Growth and Altered Phosphate Accumulation

In response to phosphate (Pi) starvation stress, plants exhibit diverse adaptive strategies, including carbohydrate accumulation and transport to roots, which are critical for Pi deficiency signaling. However, the functional characterization of sugar metabolic genes is often hindered by the infertility of null mutants, and the role of carbohydrate biosynthetic genes in phosphorus (P) homeostasis remains unclear. Here, we functionally characterized Ugp1, a highly expressed gene in rice (Oryza sativa) that encodes UDP-glucose pyrophosphorylase. Ugp1 was expressed throughout the rice plant and was transcriptionally induced by Pi starvation in shoot tissues. Localized to the cytosol, Ugp1 was found to be responsible for the biosynthesis of the major sugar sucrose. Homozygous mutation of Ugp1 resulted in an infertile phenotype, decreased sucrose content, retarded growth and increased Pi accumulation, while heterozygous Ugp1 plants exhibited intermediate phenotypes. The increased Pi accumulation in osugp1 mutants was accompanied by the upregulation of Pi starvation-responsive genes. Notably, in vivo 31P-nuclear magnetic resonance analysis revealed an increase in vacuolar and a decrease in cytoplasmic Pi concentration in osugp1 mutants. These findings indicate that Ugp1 plays a critical role in sucrose biosynthesis and is essential for sustaining normal growth and P homeostasis in rice. Its mutation will lead to impaired sucrose synthesis, retarded growth, and altered phosphorus accumulation and distribution. These results highlight the close relationship between carbon metabolism and P homeostasis, offering new perspectives for understanding the molecular mechanisms of plant responses to Pi starvation and providing a theoretical basis for future research on plant nutrient regulation.