The exine of angiosperm pollen grains is usually covered by a complex mix of metabolites including pollen-specific hydroxycinnamic acid amides (HCAAs) and flavonoid glycosides. Whereas the biosynthetic pathways resulting in the formation of HCAAs and flavonol glycosides have been characterized, it is unclear, how these compounds are transported to the pollen surface. In this report we provide several lines of evidence that AtNPF2.8, a member of the nitrate/peptide NTR/PTR family of transporters is required for accumulation and transport of pollen-specific flavonol 3-O-sophorosides, characterized by a glycosidic β-1,2-linkage, to the pollen surface of Arabidopsis. Ectopic, transient expression of this flavonol sophoroside transporter, termed AtFST1, fused to green fluorescent protein (GFP) demonstrated localization of AtFST1 at the plasmalemma in epidermal leaf cells of Nicotiana benthamiana whereas the tapetum-specific AtFST1-expression was confirmed by promAtFST1:GFP-reporter lines. In vitro characterization of AtFST1-activity was achieved by microbial uptake assays based on 14C-labeled flavonol glycosides. Finally, rescue of an fst1-line by complementation with a genomic fragment of the AtFST1 gene restored flavonol glycoside accumulation of pollen grains to wild-type levels corroborating the requirement of AtFST1 for transport of flavonol-3-O-sophorosides from the tapetum to the pollen surface.

被子植物花粉粒的外壁通常被代谢物的复杂混合物所覆盖，包括花粉特异性羟基肉桂酸酰胺（HCAAs）和类黄酮糖苷。尽管已经表征了导致HCAA和黄酮醇苷形成的生物合成途径，但是尚不清楚这些化合物如何转运至花粉表面。在这份报告中，我们提供了几条证据，证明AtNPF2.8（硝酸盐/肽NTR / PTR转运蛋白家族的成员）是花粉特异性黄酮3-O-槐糖苷（以糖苷类β- 1,2-键合到拟南芥的花粉表面。黄酮醇槐糖苷转运蛋白（称为AtFST1）的异位瞬时表达，融合到绿色荧光蛋白（GFP）上证明本尼瑟姆氏烟草表皮叶细胞中AtFST1位于质膜，而promAtFST1：GFP报告基因系证实了绒毡层特异性AtFST1的表达。AtFST1活性的体外表征是通过基于14C标记的黄酮醇苷的微生物摄取测定来实现的。最后，通过与AtFST1基因的基因组片段互补来拯救fst1品系，将花粉粒中黄酮糖苷的积累恢复至野生型水平，从而证实了AtFST1要求将黄酮醇3-O-槐糖苷从绒毡层转移至绒毛膜。花粉表面。AtFST1活性的体外表征是通过基于14C标记的黄酮醇苷的微生物摄取测定来实现的。最后，通过与AtFST1基因的基因组片段互补来拯救fst1品系，将花粉粒中黄酮糖苷的积累恢复至野生型水平，从而证实了AtFST1要求将黄酮醇3-O-槐糖苷从绒毡层转移至绒毛膜。花粉表面。AtFST1活性的体外表征是通过基于14C标记的黄酮醇苷的微生物摄取测定来实现的。最后，通过与AtFST1基因的基因组片段互补来拯救fst1品系，将花粉粒中黄酮糖苷的积累恢复至野生型水平，从而证实了AtFST1要求将黄酮醇3-O-槐糖苷从绒毡层转移至绒毛膜。花粉表面。