Phosphorus (P) is essential for plant growth and development, and the vacuole is an important organelle for phosphate storage. However, the tonoplast phosphate transporter in fleshy fruits remains unknown. In this study, based on the strawberry (Fragaria × ananassa) fruit transcriptome data, a tonoplast-localized vacuolar phosphate transporter with SPX and major facilitator superfamily domains, FaVPT1, was identified. FaVPT1 expression was highest in the fruits and could be induced by sucrose. Using transient transgenic systems in strawberry fruit, the downregulation and upregulation of FaVPT1 inhibited and promoted ripening, respectively, and affected phosphate contents, fruit firmness, sugar and anthocyanin contents, and ripening-related gene transcription. FaVPT1 could rescue Pi absorption in both yeast and the Arabidopsis atvpt1 mutant, confirming the similar function of FaVPT1 and AtVPT1, a previously identified tonoplast phosphate transporter in Arabidopsis. The Escherichia coli-expressed SPX domain of FaVPT1 could strongly bind to InsP 6 with a K d of 3.5 μM. The results demonstrate that FaVPT1 is a tonoplast phosphate transporter and regulates strawberry fruit ripening and quality, to a large extent, via sucrose.

Background Strawberry (Fragaria) is regarded as a model plant for both Rosaceae and non-climacteric fruit ripening. Although much progress has been made in identification of gene function using stable and transient genetic transformation systems in strawberry, the limitation is, more or less, are present. To this end, development of a rapid, efficient, and stable transformation system is required for strawberry research and breeding. Results Here, using diploid Hawaii-4 (Fragaria vesca) seeds and a reporter gene of CHLH (the H subunit of magnesium chelatase magnesium chelatase) key to chlorophyll synthesis, we first develop a rapid, efficient, and stable infected system by the Agrobacterium-mediated seed infection to silence the reporter gene, reaching an infection frequency with 28.3% through a series of optimization elements, including seed full imbibition and initial germination, shaking infection for 24 h, dark cultivation on MS medium for 3 d at 24 ℃, light culture on MS-Tim medium for 1 week at 24 ℃, and vector construction tagged with fluorescence label. Taken together, radicle-emergence germination seeds, appropriate Agrobacterium concentration and infection time are critical for successful infection, finally obtaining the infected kanamycin-resistant seedlings of T1 generation by infected wild seeds within 1 month and T2 generation-infected plants within 4 months. Conclusions The Agrobacterium-mediated infection of germinating seeds (AMTGS) in diploid strawberry (F. vesca) is first established, providing a useful tool for gene function identification and improved agronomic traits in strawberry.