Aphids have a mutualistic relationship with the bacterial endosymbiont Buchnera aphidicola. We previously reported seven cysteine-rich peptides in the pea aphid Acyrthosiphon pisum and named them Bacteriocyte-specific Cysteine-Rich (BCR) peptides; these peptides are exclusively expressed in bacteriocytes, special aphid cells that harbor symbionts. Similar symbiotic organ-specific cysteine-rich peptides identified in the root nodules of leguminous plants are named Nodule-specific Cysteine-Rich (NCR) peptides. NCR peptides target rhizobia in the nodules and are essential for symbiotic nitrogen fixation. A BacA (membrane protein) mutant of Sinorhizobium is sensitive to NCR peptides and is unable to establish symbiosis. Based on the structural and expressional similarities between BCR peptides and NCR peptides, we hypothesized that aphid BCR peptides exhibit antimicrobial activity, similar to some NCR peptides. We herein synthesized BCR peptides and investigated their antimicrobial activities and effects on the bacterial membrane of Escherichia coli. The peptides BCR1, BCR3, BCR5, and BCR8 exhibited antimicrobial activities with increased membrane permeability. An sbmA mutant of E. coli, a homolog of bacA of S. meliloti, was more sensitive to BCR peptides than the wild type. Our results suggest that BCR peptides have properties that may be required to control the endosymbiont, similar to NCR peptides in legumes.

中文翻译：

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豌豆蚜虫细菌细胞特异性富含半胱氨酸肽的抗菌活性

蚜虫与细菌内共生菌 Buchnera aphidicola 具有共生关系。我们之前报道了豌豆蚜虫 Acyrthosiphon pisum 中的七种富含半胱氨酸的肽，并将它们命名为细菌细胞特异性富含半胱氨酸 (BCR) 肽；这些肽仅在细菌细胞中表达，细菌细胞是具有共生体的特殊蚜虫细胞。在豆科植物的根瘤中鉴定出的类似共生器官特异性富含半胱氨酸的肽被命名为根瘤特异性富含半胱氨酸 (NCR) 肽。NCR 肽靶向根瘤中的根瘤菌，对共生固氮至关重要。中华根瘤菌的 BacA（膜蛋白）突变体对 NCR 肽敏感，无法建立共生关系。基于 BCR 肽和 NCR 肽之间的结构和表达相似性，我们假设蚜虫 BCR 肽表现出抗菌活性，类似于一些 NCR 肽。我们在此合成了 BCR 肽并研究了它们的抗菌活性和对大肠杆菌细菌膜的影响。肽 BCR1、BCR3、BCR5 和 BCR8 表现出抗菌活性，膜通透性增加。大肠杆菌的 sbmA 突变体（苜蓿根瘤菌的 bacA 的同源物）比野生型对 BCR 肽更敏感。我们的结果表明 BCR 肽具有控制内共生体可能需要的特性，类似于豆类中的 NCR 肽。BCR8 表现出抗菌活性，膜通透性增加。大肠杆菌的 sbmA 突变体（苜蓿根瘤菌的 bacA 的同源物）比野生型对 BCR 肽更敏感。我们的结果表明 BCR 肽具有控制内共生体可能需要的特性，类似于豆类中的 NCR 肽。BCR8 表现出抗菌活性，膜通透性增加。大肠杆菌的 sbmA 突变体（苜蓿根瘤菌的 bacA 的同源物）比野生型对 BCR 肽更敏感。我们的结果表明 BCR 肽具有控制内共生体可能需要的特性，类似于豆类中的 NCR 肽。