Tomato sucrose synthase SUS3 is involved in flower and seed development

Sucrose is a vital product of photosynthesis and plays important roles in plant growth and development. Sucrose synthase (SUS) is one of the major contributors in sucrose utilization. However, its roles in plant development are still not well understood. In tomato (Solanum lycopersicon) 'Moneymaker', SlSUS3 showed a relatively high expression in flowers, we then further investigated its function in the development of flowers, fruits and seeds. In flowers, SlSUS3 was highly expressed in the petal, stigma and style. SlSUS3 was localized at the plasma membrane and in the cytosol. Silencing SlSUS3 decreased the number of flowers and fruits, and the proportion of multi-petal flowers. The expression of several MADS-box transcription factor genes and the contents of soluble sugar and starch in flowers were lower in the SlSUS3-silenced plants than the wild type. Transcriptome analysis of flower buds from the SlSUS3-silenced plants and the wild type revealed that the differentially expressed genes were involved in pollen development, morphogenesis, polyamine metabolism, and secondary metabolite biosynthesis. Silencing SlSUS3 down-regulated the expression of amine oxidase genes and increased the spermidine content in flower buds, suggesting that inhibition of SlSUS3 expression may have affected flower development by regulating the polyamine content. Silencing SlSUS3 also decreased the number of developed seeds, pollen viability and germination rate, as well as the expression of genes involved in pollen development. Our results suggest that SlSUS3 regulates flower and seed development by modulating sugar and spermidine levels. This study may help better understand the role of SUS in plant development.