植物藉由光合作用產生糖類送到各個器官中轉化為生物量。研究指出SWEET糖轉運蛋白在糖的輸出機制上扮演重要角色，像是韌皮部卸載、種子的填充以及花蜜的形成，同時SWEET的表現也與病原菌的感染機制有關。然而其對作物生長的功能仍研究有限。番茄為研究果實發育及病原菌致病的模式植物，因此本研究以番茄 Micro-tom作為研究材料。利用阿拉伯芥AtSWEET1的氨基酸序列比對番茄資料庫，找到31個番茄SlSWEETs基因，並將其分成四群 (Clade I-IV)。經由qRT-PCR的分析發現番茄SlSWEET1c、1a、11a、5b 分別在根部、幼葉、成熟葉、花部有顯著高度表現，並且在不同時期的果實中發現SlSWEET1a、1b、12c有高度表現，顯示SlSWEET可能具有器官專一性的功能。此外，我們也發現番茄 Clade I SWEET1e、1f的基因座落在抗青枯病基因標記區段中 (Bwr-6)，比較三感病種以及抗病種所有基因的表現變化，發現SlSWEET1f在抗病種中感染後表現下降，而在感病種則上升。此外，當感染青枯病菌時SlSWEET3、1c在根部表現明顯被抑制。SlSWEET1c、1f、3皆屬於Clade I的SWEET，這個結果表示番茄Clade I的SWEET可能參與青枯病菌感染機制中。藉由酵母菌生長互補分析發現，Clade I、II 的SWEET對 Glucose、Galactose有轉運活性，Clade II同時也對Mannose有轉運活性，而Clade IV的SWEET則對 Fructose 以及 Mannose有轉運活性。由於SlSWEET1a在幼葉以及果實中有顯著高表現，並且對Glucose有高轉運活性，所以針對SlSWEET1a做進一步功能分析。利用碳14同位素追蹤分析發現SlSWEET1a為低親和性Glucose 專一轉運蛋白，並藉由SlSWEET1a與GFP融合蛋白的表現証實SlSWEET1a為細胞膜上的轉運蛋白。利用VIGS基因靜默技術發現抑制SlSWEET1a的表現會使幼葉中的糖含量降低，由這些結果此我們推論SlSWEET1a可能的功能為將糖輸入至幼葉中提供生長所需。目前已建立過表現及RNAi基因轉殖植物，將來會進行功能分析來釐清SlSWEET1a對番茄生長的角色。

Here, 31 SlSWEETs were identified from tomato genome and can be classed into four clades. The qRT-PCR analysis indicated that SlSWEET genes exhibited organ-specific expression pattern. Moreover, the data suggesting that clade I SlSWEETs may be involved in bacterial wilt pathogenesis. By using yeast complementary assay, the substrate-specific transport activities of SlSWEETs were also revealed. Clade I, II and IV specifically transport monosaccharide. Moreover, the C14-tracer analysis showed that SlSWEET1a is a glucose-specific transporter that is localized on the plasma membrane. When the gene expression of SlSWEET1a was reduced by VIGS (virus induced gene silence) technique, sugar contents in young leaves were significantly reduced, indicating that SlSWEET1a may play a role in glucose uptake into young leaves. Transgenic plants overexpressing SlSWEET1a have been generated and will be examined to validate SlSWEET1a function.

Aluri S, Büttner M, 2007. Identification and functional expression of the Arabidopsis thaliana vacuolar glucose transporter 1 and its role in seed germination and flowering. Proceedings of the National Academy of Sciences 104, 2537-42.
Tomato Genome Consortium, 2012. The tomato genome sequence provides insights into fleshy fruit evolution. Nature 485, 635-41.
Antony G, Zhou J, Huang S, et al., 2010. Rice xa13 recessive resistance to bacterial blight is defeated by induction of the disease susceptibility gene Os-11N3. Plant Cell 22, 3864-76.
Ayre BG, 2011. Membrane-transport systems for sucrose in relation to whole-plant carbon partitioning. Molecular Plant 4, 377-94.
Bitterlich M, Krugel U, Boldt-Burisch K, Franken P, Kuhn C, 2014. The sucrose transporter SlSUT2 from tomato interacts with brassinosteroid functioning and affects arbuscular mycorrhiza formation. Plant Journal 78, 877-89
Braun DM, Slewinski TL, 2009. Genetic Control of Carbon Partitioning in Grasses: Roles of Sucrose Transporters and Tie-dyed Loci in Phloem Loading. Plant Physiology 149, 71-81.
Burke JJ, 2007. Evaluation of Source Leaf Responses to Water-Deficit Stresses in Cotton Using a Novel Stress Bioassay. Plant Physiology 143, 108-21.
Bürkle L, Hibberd JM, Quick WP, Kühn C, Hirner B, Frommer WB, 1998. The H+-Sucrose Cotransporter NtSUT1 Is Essential for Sugar Export from Tobacco Leaves. Plant Physiology 118, 59-68.
Buttner M, 2010. The Arabidopsis sugar transporter (AtSTP) family: an update. Plant Bioogyl (Stuttg) 12 Suppl 1, 35-41.
Chen HY, Huh JH, Yu YC, et al., 2015a. The Arabidopsis vacuolar sugar transporter SWEET2 limits carbon sequestration from roots and restricts Pythium infection. Plant Journal 83, 1046-58.
Chen L-Q, 2014. SWEET sugar transporters for phloem transport and pathogen nutrition. New Phytologist 201, 1150-5.
Chen L-Q, Hou B-H, Lalonde S, et al., 2010. Sugar transporters for intercellular exchange and nutrition of pathogens. Nature 468, 527-32.
Chen LQ, Lin IW, Qu XQ, et al., 2015b. A cascade of sequentially expressed sucrose transporters in the seed coat and endosperm provides nutrition for the Arabidopsis embryo. Plant Cell 27, 607-19.
Chen LQ, Qu XQ, Hou BH, et al., 2012. Sucrose efflux mediated by SWEET proteins as a key step for phloem transport. Science 335, 207-11.
Chincinska IA, Liesche J, Krugel U, et al., 2008. Sucrose transporter StSUT4 from potato affects flowering, tuberization, and shade avoidance response. Plant Physiology 146, 515-28.
Chu Z, Yuan M, Yao J, et al., 2006. Promoter mutations of an essential gene for pollen development result in disease resistance in rice. Genes & Development 20, 1250-5.
Dinesh-Kumar SP, Anandalakshmi R, Marathe R, Schiff M, Liu Y, 2003. Virus-induced gene silencing. Methods in Molecular Biology 236, 287-94.
Doidy J, Grace E, Kühn C, Simon-Plas F, Casieri L, Wipf D, 2012. Sugar transporters in plants and in their interactions with fungi. Trends in Plant Science 17, 413-22.
Feng CY, Han JX, Han XX, Jiang J, 2015. Genome-wide identification, phylogeny, and expression analysis of the SWEET gene family in tomato. Gene 573, 261-72.
Foulkes MJ, Slafer GA, Davies WJ, et al., 2011. Raising yield potential of wheat. III. Optimizing partitioning to grain while maintaining lodging resistance. Journal of Experimental Botany 62, 469-86.
Fry SC, Aldington S, Hetherington PR, Aitken J, 1993. Oligosaccharides as signals and substrates in the plant cell wall. Plant Physiology 103, 1-5.
Gietz RD, Schiestl RH, 2007. High-efficiency yeast transformation using the LiAc/SS carrier DNA/PEG method. Nature Protocols 2, 31-4.
Giuliano G, Bartley GE, Scolnik PA, 1993. Regulation of carotenoid biosynthesis during tomato development. Plant Cell 5, 379-87.
Griffith M, Lumb C, Wiseman SB, Wisniewski M, Johnson RW, Marangoni AG, 2005. Antifreeze proteins modify the freezing process in planta. Plant Physiology 138, 330-40.
Guan YF, Huang XY, Zhu J, Gao JF, Zhang HX, Yang ZN, 2008. RUPTURED POLLEN GRAIN1, a member of the MtN3/saliva gene family, is crucial for exine pattern formation and cell integrity of microspores in Arabidopsis. Plant Physiology 147, 852-63.
Guo W-J, Nagy R, Chen H-Y, et al., 2014. SWEET17, a Facilitative Transporter, Mediates Fructose Transport across the Tonoplast of Arabidopsis Roots and Leaves. Plant Physiology 164, 777-89.
Hackel A, Schauer N, Carrari F, Fernie AR, Grimm B, Kuhn C, 2006. Sucrose transporter LeSUT1 and LeSUT2 inhibition affects tomato fruit development in different ways. Plant Journal 45, 180-92.
Hummel I, Pantin F, Sulpice R, et al., 2010. Arabidopsis Plants Acclimate to Water Deficit at Low Cost through Changes of Carbon Usage: An Integrated Perspective Using Growth, Metabolite, Enzyme, and Gene Expression Analysis. Plant Physiology 154, 357-72.
Klemens PA, Patzke K, Deitmer J, et al., 2013. Overexpression of the vacuolar sugar carrier AtSWEET16 modifies germination, growth, and stress tolerance in Arabidopsis. Plant Physiology 163, 1338-52.
Kuhn C, Hajirezaei MR, Fernie AR, et al., 2003. The sucrose transporter StSUT1 localizes to sieve elements in potato tuber phloem and influences tuber physiology and development. Plant Physiology 131, 102-13.
Lecourieux F, Kappel C, Lecourieux D, et al., 2013. An update on sugar transport and signalling in grapevine. Journal of Experimental Botany.
Lei MG, Liu YD, Zhang BC, et al., 2011. Genetic and Genomic Evidence That Sucrose Is a Global Regulator of Plant Responses to Phosphate Starvation in Arabidopsis. Plant Physiology 156, 1116-30.
Lin IW, Sosso D, Chen L-Q, et al., 2014. Nectar secretion requires sucrose phosphate synthases and the sugar transporter SWEET9. Nature 508, 546-9.
Liu Y-H, Offler CE, Ruan Y-L, 2013. Regulation of fruit and seed response to heat and drought by sugars as nutrients and signals. Frontiers in Plant Science 4.
Müller-Röber B, Sonnewald U, Willmitzer L, 1992. Inhibition of the ADP-glucose pyrophosphorylase in transgenic potatoes leads to sugar-storing tubers and influences tuber formation and expression of tuber storage protein genes. The EMBO Journal 11, 1229-38.
Pelleschi S, Rocher JP, Prioul JL, 1997. Effect of water restriction on carbohydrate metabolism and photosynthesis in mature maize leaves. Plant, Cell & Environment 20, 493-503.
Podrabsky JE, Somero GN, 2004. Changes in gene expression associated with acclimation to constant temperatures and fluctuating daily temperatures in an annual killifish. Journal of Experimental Biology 207, 2237-54.
Rennie EA, Turgeon R, 2009. A comprehensive picture of phloem loading strategies. Proceeding of the National Academy of Sciences of the United States of America 106, 14162-7.
Rolland F, Baena-Gonzalez E, Sheen J, 2006. Sugar sensing and signaling in plants: Conserved and novel mechanisms. Annual Review of Plant Biology 57, 675-709.
Sherson SM, Alford HL, Forbes SM, Wallace G, Smith SM, 2003. Roles of cell-wall invertases and monosaccharide transporters in the growth and development of Arabidopsis. Journal of Experimental Botany 54, 525-31.
Sosso D, Luo D, Li Q-B, et al., 2015. Seed filling in domesticated maize and rice depends on SWEET-mediated hexose transport. Nature Genetics 47, 1489-93.
Srivastava AC, Ganesan S, Ismail IO, Ayre BG, 2008. Functional Characterization of the Arabidopsis AtSUC2 Sucrose/H+ Symporter by Tissue-Specific Complementation Reveals an Essential Role in Phloem Loading But Not in Long-Distance Transport. Plant Physiology 148, 200-11.
Sze H, Li X, Palmgren MG, 1999. Energization of plant cell membranes by H+-pumping ATPases. Regulation and biosynthesis. The Plant Cell 11, 677-90.
Tao Y, Cheung LS, Li S, et al., 2015. Structure of a eukaryotic SWEET transporter in a homotrimeric complex. Nature 527, 259-63.
Taylor NG, Scheible WR, Cutler S, Somerville CR, Turner SR, 1999. The irregular xylem3 locus of arabidopsis encodes a cellulose synthase required for secondary cell wall synthesis. The Plant Cell 11, 769-79.
Turgeon R, 2010. The Role of Phloem Loading Reconsidered. Plant Physiology 152, 1817-23.
Turnage MA, Muangsan N, Peele CG, Robertson D, 2002. Geminivirus-based vectors for gene silencing in Arabidopsis. Plant Journal 30, 107-14.
Wang J-F, Ho F-I, Truong HTH, et al., 2013. Identification of major QTLs associated with stable resistance of tomato cultivar ‘Hawaii 7996’ to Ralstonia solanacearum. Euphytica 190, 241-52.
Wheeler GL, Jones MA, Smirnoff N, 1998. The biosynthetic pathway of vitamin C in higher plants. Nature 393, 365-9.
Wick AN, Drury DR, Nakada HI, Wolfe JB, 1957. Localization of the primary metabolic block produced by 2-deoxyglucose. The Journal of Biological Chemistry 224, 963-9.
Wingenter K, Schulz A, Wormit A, et al., 2010. Increased activity of the vacuolar monosaccharide transporter TMT1 alters cellular sugar partitioning, sugar signaling, and seed yield in Arabidopsis. Plant Physiology 154, 665-77.
Wu FH, Shen SC, Lee LY, Lee SH, Chan MT, Lin CS, 2009. Tape-Arabidopsis Sandwich - a simpler Arabidopsis protoplast isolation method. Plant Methods 5, 16.
Xu Y, Tao Y, Cheung LS, et al., 2014. Structures of bacterial homologues of SWEET transporters in two distinct conformations. Nature 515, 448-52.
Xuan YH, Hu YB, Chen L-Q, et al., 2013. Functional role of oligomerization for bacterial and plant SWEET sugar transporter family. Proceeding of the National Academy of Sciences of the United States of America 110, E3685-E94.
Yang B, Sugio A, White FF, 2006. Os8N3 is a host disease-susceptibility gene for bacterial blight of rice. Proceedings of the National Academy of Sciences 103, 10503-8.
Yano R, Nakamura M, Yoneyama T, Nishida I, 2005. Starch-related alpha-glucan/water dikinase is involved in the cold-induced development of freezing tolerance in Arabidopsis. Plant Physiology 138, 837-46.
Yin YG, Kobayashi Y, Sanuki A, et al., 2010. Salinity induces carbohydrate accumulation and sugar-regulated starch biosynthetic genes in tomato (Solanum lycopersicum L. cv. 'Micro-Tom') fruits in an ABA- and osmotic stress-independent manner. Journal of Experimental Botany 61, 563-74.
Yuan M, Chu Z, Li X, Xu C, Wang S, 2009. Pathogen-induced expressional loss of function is the key factor in race-specific bacterial resistance conferred by a recessive R gene xa13 in rice. The Plant Cell Physiology 50, 947-55.