Ministry of Agriculture Key Lab of Agricultural Entomology, Institute of Insect Sciences, Zhejiang University, 866 Yuhangtang Road, Hangzhou 310058, China.
J Insect Physiol. 2013 Nov;59(11):1095-103. doi: 10.1016/j.jinsphys.2013.08.011. Epub 2013 Sep 5.
Defensins are members of a large and diverse family of antimicrobial peptides (AMPs) containing three or four intramolecular disulfide bonds. They are widely distributed from vertebrates to invertebrates, and serve as critical defense molecules protecting the host from the invasion of pathogens or protozoan parasites. Cotesia vestalis is a small endoparasitoid wasp that lays eggs in larvae of Plutella xylostella, a cosmopolitan pest of cruciferous crops. We identified and characterized three full-length cDNAs encoding putative defensin-like peptides from C. vestalis, named CvDef1, CvDef2 and CvDef3. Phylogenetic analyses of these sequences showed that they are present in two clades, CITDs and PITDs, indicating a diversity of defensins in C. vestalis. We analyzed their expression patterns in larvae, pupae and adults by semi-quantitative RT-PCR. The results showed that CvDef1 mRNA was expressed from the end stage of the second instar larva, CvDef3 mRNA from the early stage of the second instar larva, and CvDef2 mRNA was expressed in all developmental stages of C. vestalis. Furthermore, CvDef1 showed antimicrobial activity against gram-positive and gram-negative bacteria. Growth kinetics of Staphylococcus aureus indicated that CvDef1 had much better antimicrobial ability than ampicillin, making it a potential candidate for practical use. Transmission electron microscopic (TEM) examination of CvDef1-treated S. aureus cells showed extensive damage to the cell membranes. Our results revealed the basic properties of three defensins in C. vestalis for the first time, which may pave the way for further study of the functions of defensins in parasitism and innate immunity of C. vestalis.
防御素是一大类具有多样性的抗菌肽 (AMPs) 家族成员，包含三个或四个分子内二硫键。它们广泛分布于从脊椎动物到无脊椎动物，作为宿主抵御病原体或原生动物寄生虫入侵的关键防御分子。西方草蛉是一种小型内寄生蜂，它将卵产在小菜蛾幼虫体内，小菜蛾是十字花科作物的世界性害虫。我们从西方草蛉中鉴定并表征了三个全长 cDNA，它们编码推定的防御素样肽，分别命名为 CvDef1、CvDef2 和 CvDef3。这些序列的系统发育分析表明，它们存在于两个分支，CITDs 和 PITDs，表明西方草蛉中存在防御素的多样性。我们通过半定量 RT-PCR 分析了它们在幼虫、蛹和成虫中的表达模式。结果表明，CvDef1 mRNA 从第二龄幼虫末期开始表达，CvDef3 mRNA 从第二龄幼虫早期开始表达，CvDef2 mRNA 在西方草蛉的所有发育阶段都表达。此外，CvDef1 对革兰氏阳性和革兰氏阴性细菌均具有抗菌活性。金黄色葡萄球菌的生长动力学表明，CvDef1 比氨苄西林具有更好的抗菌能力，使其成为实际应用的潜在候选物。透射电子显微镜 (TEM) 检查 CvDef1 处理的金黄色葡萄球菌细胞显示细胞膜广泛受损。我们的研究结果首次揭示了西方草蛉中三种防御素的基本特性，这可能为进一步研究防御素在西方草蛉寄生和先天免疫中的功能铺平道路。
