Darsouei Reyhaneh, Karimi Javad, Dunphy Gary B
Biocontrol and Insect Pathology Laboratory, Department of Plant Protection, School of Agriculture, Ferdowsi University of Mashhad, Mashhad, Iran.
Biocontrol and Insect Pathology Laboratory, Department of Plant Protection, School of Agriculture, Ferdowsi University of Mashhad, Mashhad, Iran.
J Insect Physiol. 2017 Aug;101:82-90. doi: 10.1016/j.jinsphys.2017.07.003. Epub 2017 Jul 14.
Xenorhabdus nematophila is a symbiotic bacterium of the entomopathogenic nematode Steinernema carpocapsae (Weiser). It produces several toxic proteins which interfere with the immune system of insects. The current study shows that purified pilin protein could be a virulence trait of X. nematophila. The fifth instar larvae of Spodoptera exigua (Hübner) was injected with purified pilin. Changes in the cellular defenses in terms of total haemocyte counts and granulocyte percentage and humoral factors including total protease, phospholipase A, and phenoloxidase activities (humoral defense) as well as the expression of the three main antimicrobial peptides attacin, cecropin, and spodoptericin were measured at specific times. The level of THC and granulocytes in larvae with different concentrations of pilin protein were less than the negative control. Also agglutination of haemocytes was observed 8-16h post-injection. The pilin protein activated phenoloxidase in the initial hour post-injection, by 2hpi, activity was stable. The activities of phospholipase A2 and protease activities reached maximum levels at 12 and 4hpi, respectively, and then decreased. The expressions of attacin, cecropin, and spodoptericin in larvae treated with pilin protein were up-regulated above that of the normal sample. The overexpression of cecropin was greater than the other antimicrobial protein mRNA transcripts. The spodoptericin expression had an irregular trend while expressions of attacin and cecropin reached maximum levels at 4hpi and then decreased. Generally, after the injection of pilin protein, the cellular and humoral immune system of S. exigua is activated but this toxin was able to inhibit them. This is the first report of the role of pilin protein when the bacterial symbiont of S. carpocapsae encounters the humoral defense of an insect.
嗜线虫致病杆菌（Xenorhabdus nematophila）是昆虫病原线虫小卷蛾斯氏线虫（Steinernema carpocapsae，Weiser）的共生细菌。它能产生多种干扰昆虫免疫系统的毒性蛋白。目前的研究表明，纯化的菌毛蛋白可能是嗜线虫致病杆菌的一种毒力特性。将纯化的菌毛蛋白注射到甜菜夜蛾（Spodoptera exigua，Hübner）的五龄幼虫体内。在特定时间测量细胞防御方面的变化，包括总血细胞计数和粒细胞百分比，以及体液因子，如总蛋白酶、磷脂酶A和酚氧化酶活性（体液防御），同时测量三种主要抗菌肽——攻击素、天蚕素和甜菜夜蛾抗菌肽的表达。不同浓度菌毛蛋白处理的幼虫中总血细胞计数和粒细胞水平低于阴性对照。注射后8 - 16小时还观察到血细胞凝集现象。菌毛蛋白在注射后最初1小时激活酚氧化酶，到注射后2小时，活性稳定。磷脂酶A2和蛋白酶活性分别在注射后12小时和4小时达到最高水平，然后下降。用菌毛蛋白处理的幼虫中攻击素、天蚕素和甜菜夜蛾抗菌肽的表达上调，高于正常样本。天蚕素的过表达大于其他抗菌蛋白的mRNA转录本。甜菜夜蛾抗菌肽的表达呈不规则趋势，而攻击素和天蚕素的表达在注射后4小时达到最高水平，然后下降。一般来说，注射菌毛蛋白后，甜菜夜蛾的细胞和体液免疫系统被激活，但这种毒素能够抑制它们。这是关于小卷蛾斯氏线虫的细菌共生体遇到昆虫体液防御时菌毛蛋白作用的首次报道。
