Identification of three prophenoloxidase‐activating factors (PPAFs) from an invasive beetle Octodonta nipae Maulik (Coleoptera: Chrysomelidae) and their roles in the prophenoloxidase activation

• Published in: Archives of insect biochemistry and physiology 2017-12, Vol.96 (4), p.n/a
• Main Authors: Zhang, HuaJian, Tang, BaoZhen, Lin, YaPing, Chen, ZhiMing, Zhang, XiaFang, Ji, TianLiang, Zhang, XiaoMei, Hou, YouMing
• Format: Article
• Language: English
• Subjects: Abundance; Activation; Amino Acid Sequence; Animals; Bacteria; Base Sequence; Catechol Oxidase - metabolism; Coleoptera - genetics; Coleoptera - immunology; Coleoptera - metabolism; Enzyme Precursors - metabolism; Gene Expression; Hemolymph; Hemolymph - enzymology; Immune response; Immune system; Immunity, Innate; Innate immunity; Insect Proteins - metabolism; Invasive insects; Melanins - metabolism; Melanization; Octodonta nipae; Phenoloxidase; Phylogeny; Prophenoloxidase; prophenoloxidase‐activating factor; Protease; Proteases; RNA Interference; Serine; Serine Endopeptidases - genetics; Serine Endopeptidases - metabolism; serine protease; serine protease homolog; Serine Proteases - metabolism; Serine proteinase; Transcription factors; Trypsin
• ISSN: 0739-4462; 1520-6327
• DOI: 10.1002/arch.21425

A typical characteristic of the insect innate immune system is the activation of the serine protease cascade in the hemolymph. As being the terminal component of the extracellular serine protease cascade in the prophenoloxidase (proPO) activating system, proPO‐activating factors (PPAFs) activated by the upstream cascade may generate active phenoloxidase, which then induces downstream melanization. In the present study, we reported three PPAFs from the nipa palm hispid beetle Octodonta nipae (Maulik) (designated as OnPPAF1, OnPPAF2, OnPPAF3). All three OnPPAFs contained a single clip domain at the amino‐terminus followed by a trypsin‐like serine protease domain at the carboxyl‐terminus, except the Ser in the active sites of OnPPAF2 and OnPPAF3 was substituted with Gly. Transcript expression analysis revealed that all OnPPAFs were highly expressed in hemolymph, whereas OnPPAF2 showed an extremely low mRNA abundance compared with that of OnPPAF1 and OnPPAF3, and that the abundance of all three OnPPAFs was dramatically increased upon bacterial challenge. Knockdown of OnPPAF1 or OnPPAF3 resulted in a reduction of hemolymph phenoloxidase activity and an inhibition of hemolymph melanization, whereas the knockdown of OnPPAF2 did not affect the proPO cascade. Our work thus implies that the three OnPPAFs may have different functions and regulation during immune responses in O. nipae.