TIL-type protease inhibitors may be used as targeted resistance factors to enhance silkworm defenses against invasive fungi. (February 2015)

• Record Type: Journal Article
• Authors: Li, Youshan; Zhao, Ping; Liu, Huawei; Guo, Xiaomeng; He, Huawei; Zhu, Rui; Xiang, Zhonghuai; Xia, Qingyou
• Is Part Of: Insect biochemistry and molecular biology. Volume 57(2015:Feb.)
• Page Start: 11
• Page End: 19
• Publication Date: 2015-02
• Subjects: Protease inhibitors -- Resistance factors -- Silkworm defenses -- Invasive fungi; FPI-F fungal protease inhibitor-F -- TIL trypsin inhibitor-like -- RACE rapid amplification of cDNA ends -- NTA nitrilotriacetic acid -- CDEP-1 cuticle-degrading protease 1 -- PPO prophenol oxidase -- rPPO recombinant prophenol oxidase -- ddH2O double-distilled water -- hpi hours postinfection -- dpi days postinfection; Insect biochemistry -- Periodicals; Insects -- Physiology -- Periodicals; Insects -- Molecular aspects -- Periodicals; Biochemistry -- Periodicals; Insectes -- Biochimie -- Périodiques; Insectes -- Composition -- Périodiques; Insectes -- Physiologie -- Périodiques; Insectes -- Aspect moléculaire -- Périodiques; Biochimie -- Périodiques; Biochemistry; Insect biochemistry; Insects -- Molecular aspects; Insects -- Physiology; Periodicals; 572.8157
• DOI: 10.1016/j.ibmb.2014.11.006
• Languages: English
• ISSNs: 0965-1748

Abstract

Abstract: Entomopathogenic fungi penetrate the insect cuticle using their abundant hydrolases. These hydrolases, which include cuticle-degrading proteases and chitinases, are important virulence factors. Our recent findings suggest that many serine protease inhibitors, especially TIL-type protease inhibitors, are involved in insect resistance to pathogenic microorganisms. To clarify the molecular mechanism underlying this resistance to entomopathogenic fungi and identify novel genes to improve the silkworm antifungal capacity, we conducted an in-depth study of serine protease inhibitors. Here, we cloned and expressed a novel silkworm TIL-type protease inhibitor, BmSPI39. In activity assays, BmSPI39 potently inhibited the virulence protease CDEP-1 of Beauveria bassiana, suggesting that it might suppress the fungal penetration of the silkworm integument by inhibiting the cuticle-degrading proteases secreted by the fungus. Phenol oxidase activation studies showed that melanization is involved in the insect immune response to fungal invasion, and that fungus-induced excessive melanization is suppressed by BmSPI39 by inhibiting the fungal cuticle-degrading proteases. To better understand the mechanism involved in the inhibition of fungal virulence by protease inhibitors, their effects on the germination of B. bassiana conidia was examined. BmSPI38 and BmSPI39 significantly inhibited the germination of B. bassiana conidia. Survival assays showed that BmSPI38 and BmSPI39 markedly improved the survival rates of silkworms, and can therefore be used as targeted resistance proteins in the silkworm. These results provided new insight into the molecular mechanisms whereby insect protease inhibitors confer resistance against entomopathogenic fungi, suggesting their potential application in medicinal or agricultural fields. Graphical abstract: Highlights: BmSPI39 displays high stability and inhibitory capacity against microbial proteases. Fungal-induced phenol oxidase activation is controlled by protease inhibitors in the silkworm. BmSPI38 and BmSPI39 suppress the conidial germination. Protease inhibitors counter the invasion of Beauveria bassiana .