Analysis of mechanism regulating high total soluble solid content in the parthenocarpic tomato fruit induced by pat-k gene

Total soluble solid (TSS) in tomatoes is an important trait that affects consumer's preference. Previous studies have observed high TSS content in parthenocarpic tomato fruits induced by a parthenocarpic gene, pat-k. However, the mechanisms regulating high TSS content remain unknown. Hence, we have investigated the water content, metabolites involved with high TSS content, and gene expression related to starch synthesis in tomato fruits to elucidate the mechanism regulating high TSS content. We have found that independent of fruit water content, parthenocarpic fruits induced by pat-k had higher TSS content than pollinated fruits on Pat-k homozygous plants. Additionally, metabolome analysis of mature fruits has revealed that fructose influenced the difference in TSS content between pollinated fruits on Pat-k homozygous plants and the parthenocarpic fruits on pat-k homozygous plants. Furthermore, high performance liquid chromatography (HPLC) analysis showed that not only fructose contents but also glucose contents were higher in the parthenocarpic fruits on pat-k homozygous plants than pollinated fruits on Pat-k homozygous plants, suggesting that increases in these sugar contents influenced the high TSS content in the pat-k-induced parthenocarpic fruits. We also have found that parthenocarpic fruits had high starch content and upregulated Sus4, which is involved in starch synthesis, during the early stages of fruit development. Since previous reports have suggested that high starch content during the early stages of fruit development attributed to high sugar content in mature tomato fruits, our results suggest that high accumulation of starch in young fruits could be involved with high TSS content in parthenocarpic fruits induced by pat-k.