Serpin–4 Facilitates Baculovirus Infection by Inhibiting Melanization in Asian Corn Borer, Ostrinia furnacalis (Guenée)

Abstract

Phenoloxidase (PO)–catalyzed melanization is a vital immune response in insects for defense against pathogen infection. This process is mediated by clip domain serine proteases and regulated by members of the serpin superfamily. We here revealed that the infection of Autographa californica multicapsid nucleopolyhedrovirus (AcMNPV) significantly inhibited the PO activity in Ostrinia furnacalis hemolymph and induced the expression of O. furnacalis serpin–4. Addition of recombinant serpin-4 protein to O. furnacalis hemolymph resulted in a great increase of AcMNPV copies. Serpin-4 significantly suppressed the PO activity and the amidase activity in cleaving colorimetric substrate IEARpNA (IEARase activity) of hemolymph. Further experiments indicated it formed covalent complexes with three serine proteases (SP1, SP13 and SP105) and prevented them from cleaving their cognate downstream proteases in vitro. Altogether, O. furnacalis melanization restricted AcMNPV replication and serpin-4 facilitated AcMNPV infection by inhibiting serine proteases, SP1, SP13, and SP105 which were all involved in the melanization response.

Rice ragged stunt virus mediates immune responses in Nilaparvata lugens against Metarhizium anisopliae YTTR infection: evidence from two novel genes NlK-serpin and NlVenomase

“…Such synergistic effect from the combination of dsRNA with M. anisopliae YTTR infection causing more insects to death has been found in other studies on BPH (Hu et al, 2022;Pan et al, 2016), Acyrthosiphon pisum (Zhang et al, 2022;Ye et al, 2022) and Anthonomus grandis (Moreira-Pinto et al, 2021). In our study, when the expression of NlK-serpin and NlVenomase been silenced with RNAi, PO activity and AMPs showed different degree responses implying that NlK-serpin and NlVenomase may regulate PPO activation and the AMPs production (Patel, 2017;Ji et al, 2022;. In RRSV-free BPHs, combined treatment of dsNlVenomase with M. anisopliae YTTR infection caused highest mortality (Fig.…”

“…In insect innate immunity, serine protease cascade plays a vital role by regulating AMPs production, PPO activation, and melanization cascade to ght against alien pathogens invasion and sustain insects' survival (Kanost and Jiang, 2015;Patel, 2017;Heng et al, 2022;Ji et al, 2022). In this study, a clip domain serine protease, named Venomase (NlVenomase) and a Kunitz-type serine protease inhibitor (NlK-serpin) were cloned in BPH (Fig.…”

The immune response mechanism of Nilaparvata lugens against a combined infection of rice ragged stunt virus and Metarhizium anisopliae

“…68 In our study, when the expression of NlKPI and NlVenomase was silenced with RNAi, PO activity and AMPs showed different degree responses after treatment with M. anisopliae YTTR, implying that NlKPI and NlVenomase may regulate PPO activation and AMP production of BPH to protect against M. anisopliae YTTR infection. 21,23,46 In the dsEGFP treatment, after infection by EPF, PO activity was elevated in both RRSV-carrying and RRSV-free BPHs (Fig. 8).…”

“…In insect innate immunity, serine protease cascade plays a vital role by regulating AMP production, PPO activation, and melanization cascade to fight against alien pathogen invasion and sustain insect survival. 17,21,23,45,46 In this study, a clip domain serine protease, named Venomase (NlVenomase), and a Kunitz-type serine protease inhibitor (NlKPI) were cloned in BPHs (Fig. S1).…”

“…54,55 Hence, we speculated these two genes play an immune role against entomopathogenic fungus and participate in the immune process of BPHs against the co-infection with RRSV and M. anisopliae YTTR. 46,54,55 RNAi is an efficient way to explore gene functions and the RNAigenerated bio-pesticides have great potential for sustainable pest management. [56][57][58] BPHs possess systematic RNAi 59 and many studies have proved that dsRNA has strong interference efficiency in suppressing the expression of the target gene in BPHs.…”