Nature2014-06-18 5:52 PM

SWEET9蔗糖运输蛋白是花蜜分泌的关键 Nectar secretion requires sucrose phosphate synthases and the sugar transporter SWEET9


花蜜在植物与昆虫之间的相互作用中是一个重要因素,介导授粉和防卫性互惠。花蜜的功能和组成已很清楚,但花蜜分泌的机制此前仍不确定。在对三种开花植物所做的这项研究中,Wolf Frommer及同事发现,蔗糖磷酸盐合成酶在花蜜中高度表达,是花蜜的蔗糖成分的合成所必需的。运输蛋白SWEET9介导蔗糖从蜜腺薄壁组织中的生成点向蜜腺的细胞外空间的输出。


Angiosperms developed floral nectaries that reward pollinating insects. Although nectar function and composition have been characterized, the mechanism of nectar secretion has remained unclear. 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.






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