Tonoplast sugar transporter <i>PtTST1.1</i> promotes shoot growth and wood production through modulating sugar metabolism in Shanxin Yang ( <i>Populus davidiana</i> × <i>Populus bolleana</i> )

BACKGROUND AND AIMS: Tonoplast sugar transporters (TSTs) transport sugar into the vacuole and regulate intracellular sugar distribution. However, their functions in woody plants are not fully studied. METHODS: In this study, transgenic poplar plants with constitutive and inducible overexpression of PtTST1.1 were generated, as well as the phenotypes and gene expression levels of transgenic lines were observed. KEY RESULTS: PtTST1.1 exhibited constitutive expression across diverse tissues and organs, with high expression in phloem cells and old leaves. Constitutive expression of PtTST1.1 in Arabidopsis tst1-2 mutant rescued its restrained growth inhibition. Overexpression of PtTST1.1 in poplar significantly elevated biomass production and shoot growth. Transgenic poplars showed increased stem diameter, plant height, and shoot and root fresh weight, with accelerated wood formation and concurrently elevated cellulose and lignin contents. Transcriptome analysis indicated that PtTST1.1 overexpression impacted the processes of phosphorylation, the metabolic pathways of carbohydrates, and the expressions of carbohydrate metabolic and transport genes in transgenic plants. Further yeast two-hybrid assays uncovered that PtTST1.1 interacted with an auxin-induced protein PtAIR12 to regulate the growth of poplar trees. These findings suggest that PtTST1.1 can be used as a biotechnological target for xylem productivity augmentation in engineered tree species. CONCLUSIONS: We explored the function of PtTST1.1 in growth and secondary xylem development in hybrid poplar (Populus davidiana × Populus bolleana). Our findings indicated that the influence on carbohydrate metabolism and growth enhancement in PtTST.1 overexpressing lines was evident from elevated sucrose and glucose levels as well as increase in plant height, stem diameter, and the number and size of xylem cells occurs through accelerated wood formation with higher content of cell wall polymers. Furthermore, our research uncovered an interaction between PtTST1.1 and PtAIR12, which together regulated the growth of poplar trees.