醣類在植物生長中為主要的能量來源，供給植物器官發育，包含果實。番茄為世界經濟作物之一，然而其果實的醣類供給機制了解甚少。近年研究指出SWEETs醣轉運蛋白活性調控胚乳的充實度、種子的發育，很可能對果實發育扮演關鍵角色，值得探究。當分析所有SWEETs在不同生長階段番茄果實的表現量，發現屬於Clade III的SlSWEET12c在果實發育第35天以及 SlSWEET15在果實發育第21天分別具有極高度表現。酵母菌互補生長分析及碳-14同位素追蹤實驗結果得知SlSWEET12c對於蔗糖有微弱卻專一性的運輸能力。觀察分別表現SlSWEET12c/15-GFP綠螢光融合蛋白得知兩者皆表現在酵母菌及植物的液胞內，顯示其功能可能與液胞醣累積有關。分析SlSWEET12c/15-GUS融合蛋白轉植株則發現SlSWEET12c/15蛋白大量累積在種子外皮，同時可能些微表現於果肉及其維管束。為了確認其生理功能，利用CRISPR/Cas 9分別建立SlSWEET12c/15單突變株，我們發現slsweet15突變會抑制果實及種子發育與充實，這些結果顯示SlSWEET15為種子充實重要機制，其功能可能為位於液胞膜上調控種子的蔗糖供給以利果實充實。

Sugar is an important energy source during plant development and serve as nutrients to organ development, including fruits. Tomato is an important economic fruit crop in the world, yet the mechanism of sugar supply in fruits is still unclear. Studies indicate that SWEET (Sugars Will Eventually be Exported Transporters) sugar transporters regulated seed filling in Arabidopsis, and may involve in development of tomato fruits. Here, by using quantitative PCR, we have discovered that SlSWEET12c was specifically highly expressed in 35-day-old fruits, and SlSWEET15 was highly expressed 21-day-old fruits. Yeast complementation growth assay and radio-tracer uptake assay suggested that SlSWEET12c exhibited weak but specific transport activity to sucrose. Localization of SlSWEET12c/15-GFP in yeast and plant cell vacuoles suggested their putative functions in vacuolar sugar accumulation. Tissue-specific expression of SlSWEET12c/15-GUS fusion proteins were observed in transgenic tomato plants. We discovered that SlSWEET12c/15 proteins were mainly accumulated in seed coat and less in flesh and vascular bundle. To confirm its physiological function, knockout mutant lines using CRISPR/cas9 system were generated. We found that in slsweet15 mutant, fruits development and seed filling were inhibited. These results imply that SlSWEET15 may function at vacuolar membrane to regulate sucrose in seeds and supply for fruits development.

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