title: Serine proteases SP1 and SP13 mediate the melanization response of Asian corn borer, Ostrinia furnacalis, against entomopathogenic fungus Beauveria bassiana.
abstract: Exposure to entomopathogenic fungi is one approach for insect pest control. Little is known about the immune interactions between fungus and its insect host. Melanization is a prominent immune response in insects in defending against pathogens such as bacteria and fungi. Clip domain serine proteases in insect plasma have been implicated in the activation of prophenoloxidase, a key enzyme in the melanization. The relationship between host melanization and the infection by a fungus needs to be established. We report here that the injection of entomopathogenic fungus Beauveria bassiana induced both melanin synthesis and phenoloxidase activity in its host insect, the Asian corn borer, Ostrinia furnacalis (Guenée). qRT-PCR analysis showed several distinct patterns of expression of 13 clip-domain serine proteases in response to the challenge of fungi, with seven increased, two decreased, and four unchanged. Of special interest among these clip-domain serine protease genes are SP1 and SP13, the orthologs of Manduca sexta HP6 and PAP1 which are involved in the prophenoloxidase activation pathway. Recombinant O. furnacalis SP1 was found to activate proSP13 and induce the phenoloxidase activity in corn borer plasma. Additionally, SP13 was determined to directly cleave prophenoloxidase and therefore act as the prophenoloxidase activating protease. Our work thus reveals a biochemical mechanism in the melanization in corn borer associated with the challenge by B. bassiana injection. These insights could provide valuable information for better understanding the immune responses of Asian corn borer against B. bassiana.
authors.affiliation: Department of Entomology, College of Agriculture and Biotechnology, China Agricultural University, Beijing, China.
authors.forename: Yuan
authors.initials: Y
authors.lastname: Chu
authors.affiliation: State Key Laboratory for Biology of Plant Diseases and Insect Pests, Institute of Plant Protection, Chinese Academy of Agricultural Sciences, Beijing, China.
authors.forename: Yang
authors.initials: Y
authors.lastname: Liu
authors.affiliation: Department of Entomology, College of Agriculture and Biotechnology, China Agricultural University, Beijing, China.
authors.forename: Dongxu
authors.initials: D
authors.lastname: Shen
authors.affiliation: Department of Entomology, College of Agriculture and Biotechnology, China Agricultural University, Beijing, China.
authors.forename: Fang
authors.initials: F
authors.lastname: Hong
authors.affiliation: State Key Laboratory for Biology of Plant Diseases and Insect Pests, Institute of Plant Protection, Chinese Academy of Agricultural Sciences, Beijing, China.
authors.forename: Guirong
authors.initials: G
authors.lastname: Wang
authors.affiliation: Department of Entomology, College of Agriculture and Biotechnology, China Agricultural University, Beijing, China. Electronic address: anchunju@cau.edu.cn.
authors.forename: Chunju
authors.initials: C
authors.lastname: An
mesh_terms: D000818:Animals; D052982:Beauveria / Q000276:immunology; D006790:Host-Parasite Interactions / Q000502:physiology*; D015151:Immunoblotting; D019476:Insect Proteins / Q000378:metabolism*; D007915:Lepidoptera / Q000201:enzymology* / Q000276:immunology / Q000469:parasitology*; D008543:Melanins / Q000378:metabolism; D000073718:Pancreatitis-Associated Proteins; D010572:Pest Control, Biological / Q000379:methods; D016133:Polymerase Chain Reaction; D057057:Serine Proteases / Q000378:metabolism*
chemical_list: D019476:Insect Proteins; D008543:Melanins; D000073718:Pancreatitis-Associated Proteins; C000612141:REG3A protein, human; D057057:Serine Proteases
keywords: Clip domain serine protease; Entomopathogenic fungus; Melanization; Ostrinia furnacalis; Proteolytic cascade