Uchi Nahoko, Fukudome Mitsutaka, Nozaki Narumi, Suzuki Miyuzu, Osuki Ken-Ichi, Shigenobu Shuji, Uchiumi Toshiki
Graduate School of Science and Engineering, Kagoshima University.
National Institute for Basic Biology.
Microbes Environ. 2019 Jun 27;34(2):155-160. doi: 10.1264/jsme2.ME18148. Epub 2019 Mar 21.
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.
蚜虫与细菌内共生体蚜虫内共生菌有着互利共生关系。我们之前报道了豌豆蚜中的7种富含半胱氨酸的肽，并将它们命名为菌细胞特异性富含半胱氨酸（BCR）肽；这些肽仅在菌细胞中表达，菌细胞是蚜虫体内容纳共生体的特殊细胞。在豆科植物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。中华根瘤菌的一个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肽在结构和表达上的相似性，我们推测蚜虫的BCR肽具有抗菌活性，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以及对大肠杆菌细菌膜的影响。BCR1、BCR3、BCR5和BCR8肽表现出抗菌活性，且膜通透性增加。大肠杆菌的一个sbmA突变体，它是苜蓿中华根瘤菌bacA的同源物，对BCR肽比野生型更敏感。我们的结果表明，BCR肽具有控制内共生体可能需要的特性，类似于豆科植物中的NCR肽。
