Department of Biology, University of Miami, Coral Gables, FL 33146.
Institute for Cell & Molecular Biosciences, Faculty of Medical Sciences, Newcastle University, NE2 4HH, Newcastle upon Tyne, United Kingdom.
Proc Natl Acad Sci U S A. 2019 Aug 6;116(32):16003-16011. doi: 10.1073/pnas.1906223116. Epub 2019 Jul 23.
Plant sap-feeding insects are widespread, having evolved to occupy diverse environmental niches despite exclusive feeding on an impoverished diet lacking in essential amino acids and vitamins. Success depends exquisitely on their symbiotic relationships with microbial symbionts housed within specialized eukaryotic bacteriocyte cells. Each bacteriocyte is packed with symbionts that are individually surrounded by a host-derived symbiosomal membrane representing the absolute host-symbiont interface. The symbiosomal membrane must be a dynamic and selectively permeable structure to enable bidirectional and differential movement of essential nutrients, metabolites, and biosynthetic intermediates, vital for growth and survival of host and symbiont. However, despite this crucial role, the molecular basis of membrane transport across the symbiosomal membrane remains unresolved in all bacteriocyte-containing insects. A transport protein was immunolocalized to the symbiosomal membrane separating the pea aphid from its intracellular symbiont The transporter, nonessential amino acid transporter 1, or ApNEAAT1 (gene: ), was characterized functionally following heterologous expression in oocytes, and mediates both inward and outward transport of small dipolar amino acids (serine, proline, cysteine, alanine, glycine). Electroneutral ApNEAAT1 transport is driven by amino acid concentration gradients and is not coupled to transmembrane ion gradients. Previous metabolite profiling of hemolymph and bacteriocyte, alongside metabolic pathway analysis in host and symbiont, enable prediction of a physiological role for ApNEAAT1 in bidirectional host-symbiont amino acid transfer, supplying both host and symbiont with indispensable nutrients and biosynthetic precursors to facilitate metabolic complementarity.
植物汁液取食昆虫分布广泛，尽管它们专门以缺乏必需氨基酸和维生素的贫瘠饮食为食，但仍进化到能够占据多样化的环境小生境。它们的成功依赖于它们与微生物共生体之间的共生关系，这些共生体栖息在专门的真核细菌细胞内。每个细菌细胞都充满了共生体，每个共生体都被宿主衍生的共生体膜所包围，代表着绝对的宿主-共生体界面。共生体膜必须是一个动态的、具有选择性渗透性的结构，才能使必需的营养物质、代谢物和生物合成中间体双向和差异地移动，这对宿主和共生体的生长和存活至关重要。然而，尽管这一角色至关重要，但在所有含有细菌细胞的昆虫中，共生体膜的分子基础仍然没有得到解决。一种转运蛋白被免疫定位到豌豆蚜与其细胞内共生体之间的共生体膜上。这种转运蛋白，非必需氨基酸转运体 1 或 ApNEAAT1（基因：），在异源表达于卵母细胞后具有功能特征，并介导小偶极氨基酸（丝氨酸、脯氨酸、半胱氨酸、丙氨酸、甘氨酸）的内外转运。电中性的 ApNEAAT1 转运由氨基酸浓度梯度驱动，不与跨膜离子梯度偶联。之前对半血淋巴和细菌细胞的代谢物分析，以及对宿主和共生体的代谢途径分析，使我们能够预测 ApNEAAT1 在宿主-共生体双向氨基酸转移中的生理作用，为宿主和共生体提供不可或缺的营养物质和生物合成前体，以促进代谢互补。
