Nectar secretion requires sucrose phosphate synthases and the sugar transporter SWEET9
Nectar secretion requires sucrose phosphate synthases and the sugar transporter SWEET9
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DOI：
10.1038/nature13082
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发表时间：
2014-04-24
期刊：
影响因子：
64.8
通讯作者：
Frommer, Wolf B.
中科院分区：
文献类型：
--
作者：
Lin, I. Winnie;Sosso, Davide;Frommer, Wolf B.
被子植物发育了花蜜来奖励传粉昆虫(1)。虽然花蜜的功能和成分已经被描述，但花蜜分泌的机制仍然不清楚(2)。我们在拟南芥（Arabidopsis thaliana）、rapa（芸苔（Brassica rapa））和Nicotiana attenuata（雌蕊蜜腺）这三种植物中发现了SWEET9作为蜜腺特异性糖转运蛋白。我们发现SWEET9对花蜜的产生至关重要，可以作为外排转运体发挥作用。我们还发现，编码蔗糖生物合成关键酶的蔗糖磷酸合酶基因在蜜腺中高度表达，其表达也是花蜜分泌所必需的。综上所述，这些数据与蔗糖在蜜腺薄壁中合成并随后通过SWEET9分泌到细胞外空间的模型一致，在那里蔗糖被一种胞浆转化酶水解，产生蔗糖、葡萄糖和果糖的混合物。SWEET9用于蔗糖出口可能是一个关键的创新，可能与核心株的进化相吻合，并有助于花蜜分泌的进化，以奖励传粉者。
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.