The effect of pilin protein of Xenorhabdus nematophila on cellular and humoral defensive system in Spodoptera exigua larvae

عنوان دوره: دومین کنگره بین المللی حشره شناسی ایران

Reyhaneh Darsouei؛ Javad Karimi

Xenorhabdus nematophila is a symbiotic bacterium of entomopathogenic nematode, Steinernema carpocapsae. It produces several toxic proteins which interfere with the immune system of insects. Here, we have shown that purified pilin protein could be involved as a virulence trait of X. nematophila during pathogenesis. Here, pilin protein purified from culture medium of X. nematophila and then three concentrations 5, 10, and 15 mg/ml injected to fifth instar larvae of Spodoptera exigua (Hübner). Then fluctuation of total haemocyte counts (THC) and granulocyte percentage (cellular defense) as well, protease, phospholipase A2 (PLA2), and phenoloxidase (PO) activities (humoral defense) were surveyed at different times. Also, the fold change expression of three main antimicrobial peptides (AMPs) including attacin, cecropin, and spodoptericin were measured. The THC population and number of granulocytes in larvae treated with different concentrations of pilin protein were less than the negative control. The pilin protein activate PO, PLA2 and protease enzymes. Phenoloxidase activate in the initial hour post injection (hpi) but at 2 hpi its fluctuation was stable. Also, the activities of PLA2 and protease reached the maximum level at 12 and 4 hpi respectively, and then decreased. The expression of attacin, cecropin, and spodoptericin in the larvae treated with pilin protein was up-regulated above that of the normal sample. Attacin and cecropin expression reach the maximum level at 4 hpi and then decreased. While, The spodoptericin expression had an irregular trend. The cecropin expression was more than other AMPs. Attacin, cecropin, and expression after injection of 10 mg/ml toxin protein were 66±1, and 403±1 fold change greater than normal sample, respectively. Generally, pilin protein was able to suppress cellular and humoral defense. The finding of the current work provides the first insight into the role of pilin protein when the bacterial symbiont of Steinernema carpocapsae (Weiser) encounters the humoral defense of an insect.

Antimicrobial peptides؛ Cellular defense؛ Insect pathology؛ Phenoloxidae؛ Phospholipase A2؛ Protease