Nectar secretion requires sucrose phosphate synthases and the sugar transporter SWEET9

• Published in: Nature (London) Vol. 508; no. 7497; pp. 546 - 549
• Main Authors: Lin, I Winnie, Sosso, Davide, Chen, Li-Qing, Gase, Klaus, Kim, Sang-Gyu, Kessler, Danny, Klinkenberg, Peter M., Gorder, Molly K., Hou, Bi-Huei, Qu, Xiao-Qing, Carter, Clay J., Baldwin, Ian T., Frommer, Wolf B.
• Format: Journal Article
• Language: English
• Published: London Nature Publishing Group UK 24.04.2014; Nature Publishing Group
• Subjects: 13/89; 14/19; 14/33; 14/35; 38/89; 38/90; 631/449/448/2651; 631/80/2373; 9/10; Alkyl and Aryl Transferases - metabolism; Animals; Arabidopsis - cytology; Arabidopsis - enzymology; Arabidopsis - genetics; Arabidopsis - metabolism; Arabidopsis Proteins - metabolism; Arabidopsis thaliana; beta-Fructofuranosidase - metabolism; Biological transport, Active; Biosynthesis; Botanical research; Brassica rapa - anatomy & histology; Brassica rapa - enzymology; Brassica rapa - metabolism; Carbohydrate Metabolism; Evolution; Extracellular Space - metabolism; Flowers & plants; Flowers - physiology; Glucose; Glucosyltransferases - genetics; Glucosyltransferases - metabolism; HEK293 Cells; Humanities and Social Sciences; Humans; letter; Membrane Transport Proteins - metabolism; multidisciplinary; Nicotiana - anatomy & histology; Nicotiana - enzymology; Nicotiana - metabolism; Oocytes; Physiological aspects; Plant nectar; Plant Nectar - biosynthesis; Plant Nectar - metabolism; Plant Proteins - metabolism; Plant reproduction; Pollination; Protein Transport; Rape (Plant); Science; Sequence Homology; Starch - metabolism; Sucrose; Sucrose - metabolism; Sugar; Tobacco (Plant); Xenopus; United States
• ISSN: 0028-0836; 1476-4687
• DOI: 10.1038/nature13082

Although nectar is known to be important, for example in plant–insect interactions, little has been known about the mechanism of its secretion; sucrose phosphate synthases are now reported to be essential for the synthesis of the sucrose component of nectar and the transporter protein SWEET9 is shown to mediate sucrose export into the extracellular space of the nectary. SWEET9 sucrose transporter key to nectar secretion Nectar is an important factor in interactions between plants and insects, mediating both pollination and defensive mutualisms. The function and composition of floral nectaries have been well characterized, but the mechanism of nectar secretion has remained elusive. In a study of three flowering plant species, Wolf Frommer and colleagues show that sucrose phosphate synthases are highly expressed in floral nectaries and are essential for the synthesis of the sucrose component of nectar. The transporter protein SWEET9 mediates sucrose export from the site of production, in the nectary parenchyma, to the extracellular space of the nectary. Angiosperms developed floral nectaries that reward pollinating insects 1 . Although nectar function and composition have been characterized, the mechanism of nectar secretion has remained unclear 2 . Here we identify SWEET9 as a nectary-specific sugar transporter in three eudicot species: Arabidopsis thaliana , Brassica rapa (extrastaminal nectaries) and Nicotiana attenuata (gynoecial nectaries). We show that SWEET9 is essential for nectar production and can function as an efflux transporter. We also show that sucrose phosphate synthase genes, encoding key enzymes for sucrose biosynthesis, are highly expressed in nectaries and that their expression is also essential for nectar secretion. Together these data are consistent with a model in which sucrose is synthesized in the nectary parenchyma and subsequently secreted into the extracellular space via SWEET9, where sucrose is hydrolysed by an apoplasmic invertase to produce a mixture of sucrose, glucose and fructose. The recruitment of SWEET9 for sucrose export may have been a key innovation, and could have coincided with the evolution of core eudicots and contributed to the evolution of nectar secretion to reward pollinators.