郭瑋君 教授

學群：農業及海洋生物科技產業學群

研究專長：植物逆境生理、植物醣轉運生理、生物奈米粒子應用

E-mail：wjguo@mail.ncku.edu.tw

研究室：89705

Tel：+886-6-2757575#58212

醣是植物所有生化反應的能量來源，同時也扮演訊息傳遞的功能。如何促進作物分配醣至採收器官為農作物產量的關鍵問題，而位於膜上之醣轉運蛋白扮演關鍵的調控角色。研究顯示SWEET糖轉運蛋白對器官的糖輸出、積儲-供源碳分配等，皆扮演核心糖分配角色。因此，本實驗室的長期目標為透由分子生物方法及基因編輯策略來剖析驗証蕃茄中SWEET機制對果實發育及生產品質的重要性及其調控。此外，近幾年氣候變遷，如高溫、淹水等環境逆境，已嚴重衝擊糧食生產，加遽病蟲害發生。研究也發現植物糖分配與其逆境抗性相關，因此也將進一步探究SWEET機制在番茄面對環境逆境時其功能及調控，以期應用於分子育種培育韌性品種。

	Vigorous vegetative growth is the foundation for high-yield reproductive growth. If more sugars can be provided during leaf development, a better leaf growth could contribute to subsequent fruit development. Using gene expression analysis, we discover that SlSWEET1a is highly expressed in young tomato leaves. Using the VIGS strategy and molecular biological analysis methods, we show that SlSWEET1a functions on the cell membranes of phloem parenchyma cells in young leaves. Its expression is increased with sugar unloading activity. When sucrose is released from the phloem into the apoplasm, it will be hydrolyzed into glucose and fructose. At this time, SlSWEET1a assists the rapid import of glucose into parenchyma cells to maintain the sucrose concentration gradient, so as to promote the continuous sugar unloading to support the growth of young leaves (Ho et al. 2019).
	The development of reproductive organs, such as flowers, is the determinant of tomato fruit yield. We therefore explored the sugar transport mechanism that unloads sugars to flowers. Our results showed that SlSWEET5b is greatly expressed in mature flowers, especially in the cell membrane of mature pollen and anther phloem. Using the RNAi strategy in transgenic tomato plants, we reveal the key role of SlSWEET5b in pollen maturation. When sucrose is released from SE-CC cells and hydrolyzed into glucose and fructose in anther apoplasm, SlSWEET5b is located on the plasma membrane of parenchyma to promote rapid import of monosaccharides into anther cells.  More importantly, when these monosaccharides are distributed into loculus, the membrane-localized SlSWEET5b transporter is the core import mechanism to import monosaccharides that are required for pollen maturation. A functional mutation in SlSWEET5b will induce male sterility and inhibit fruit production in tomato (Ko et al. 2022).
	Fruit development is the final determinant of tomato yield and quality. Especially, sweetness of a fruit is directly related to sugar accumulation. We found that SlSWEET15 is distinctly expressed in the early stage of fruit development, in particular in vascular tissues of the pericarp and the seed coat. By characterizing CRISPR/Cas9 mutants, we confirmed that SlSWEET15 is the key mechanism for sugar unloading in tomato fruits. When sucrose is allocated to fruit phloem, SlSWEET15 is located on the plasma membrane of phloem SE-CC and neighboring SPC cells to mediate continuous sucrose export and import to support fruit growth. In addition, SlSWEET15 is also located on the membrane of seed coat to facilitate the import of sucrose into the developing seed for its carbon source. Therefore, its absence results in smaller fruits and severe seed abortion. This is the first time to reveal the sugar unloading mechanism in fruit (Ko et al., 2021). In the future, we will further investigate the possibility to enhance SlSWEET15 expression to promote fruit development in commercial cultivars.