淹水經常在作物生產期間釀成農產損失慘重。因淹沒導致植物缺氧且光合作用受限，有效的糖分配對於後續存活將非常重要。然而影響淹沒耐受性的糖轉運機制仍未闡明。先前轉錄組分析的研究表明，阿拉伯芥糖轉運蛋白SWEET可能參與水澇逆境下的糖分配，值得進一步研究。 AtSWEET2和AtSWEET16/17在淹沒過程中分別被誘導和抑制表達。初步觀察到atsweet16/17雙突變株在淹沒逆境後的恢復較差，顯示液泡膜上的AtSWEET16/17可能參與恢復期的糖分配。為應用在農作物，也探討番茄SWEET與淹沒耐受性的關聯。淹沒後在黑暗和缺氧的共同影響下，番茄供源器官和積儲器官中的葡萄糖、果糖和蔗糖含量均顯著降低9成，可見淹沒逆境造成嚴重的糖飢餓。此時在番茄31個SWEET中，SlSWEET2a-2在根、莖和葉中顯著受淹沒逆境誘導高達100倍。為了解SlSWEET2a-2的組織特異性功能，已建構表現SlSWEET2a-2-GUS的番茄轉植株，將進行觀察。因SlSWEET2a-2-GFP主要表現在阿拉伯芥原生質體的液泡膜上，表明SlSWEET2a-2可能在淹沒逆境時從液泡中輸出糖以提供碳源。為驗證此生理功能，本研究以CRISPR/ Cas9系統建立slsweet2a-2突變番茄株，並已篩選到含片段剔除之同型合子T1突變株，其耐水性的表徵正在分析中。期許將來本研究成果能作為耐淹沒作物的育種參考。

Flooding constantly causes severe yield loss during crop production. As submergence leads to hypoxia and limits photosynthesis in plants, efficient sugar distribution would be important for subsequent survival of crops. However, the sugar transport mechanism involving flooding tolerance is hardly understood. Previous studies using transcriptomic profiling suggest that Arabidopsis SWEETs (Sugars Will Eventually be Exported Transporters) may be involved in sugar allocation during waterlogging and deserves further investigation. AtSWEET2 and AtSWEET16/17 was induced and reduced, respectively, during submergence. Preliminary observation demonstrated that the recovery rate of atsweet16/17 double knockout mutants was significantly reduced after submergence. This result suggests that vacuolar AtSWEET16/17 may be involved in sugar distribution for recovery. For future application in crop production, correlation of SlSWEET expression and submergence tolerance was also examined in tomato plants. Upon submergence, combining darkness and hypoxia, contents of sucrose, glucose and fructose in both source and sink organs were all significantly decreased. In addition, SlSWEET2a-2 expression was highly induced up to 100-fold in roots, stems and leaves during submergence. To address tissue-specific function of SlSWEET2a-2, we are generating transgenic tomato plants expressing the SlSWEET2a-2-GUS fusion proteins. Localization of SlSWEE2a-2-GFP to the tonoplast membrane of Arabidopsis protoplasts suggested that SlSWEET2a-2 may be involved in sugar export from vacuole to support carbon under submergence. In order to confirm its physiological function, slsweet2a-2 knockout tomato plants were generated by using the clustered regularly interspaced short palindromic repeats (CRISPR) /CRISPR-associated protein 9 (Cas9) system. Characterization of homozygous deleted mutant lines for their flooding tolerance is in progress. We expect our results may contribute to breeding of submergence-tolerant crops in the future.

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