Abstract
Simple SummaryInsect serpins play a vital role in the defense mechanism of insects, especially in the Toll pathway and PPO (prophenoloxidase) cascade. In this study, we provided an answer to the open question of whether serpin1 was involved in the humoral immune responses of Locusta migratoria manilensis. We identified a new Lmserpin1 gene from L. migratoria manilensis and investigated its expression profiles in all examined stages and tissues. Meanwhile, by interfering with Lmserpin1 gene, we examined the mortality of L. migratoria manilensis under Metarhizium anisopliae infection, as well as the activities of protective enzymes and detoxifying enzymes and the expression level of three immune-related genes (PPAE (prophenoloxidase-activating enzyme), PPO, and defensin). The results indicated that Lmserpin1 gene up-regulated the immune responses of L. migratoria manilensis and inhibited the infection of M. anisopliae. Our results are of great importance for better understanding of the mechanism characterization of Lmserpin1 in L. migratoria manilensis.Serine protease inhibitors (Serpins) are a broadly distributed superfamily of proteins that exist in organisms with the role of immune responses. Lmserpin1 gene was cloned firstly from Locusta migratoria manilensis and then was detected in all tested stages from eggs to adults and six different tissues through qRT-PCR analysis. The expression was significantly higher in the 3rd instars and within integument. After RNAi treatment, the expression of Lmserpin1 was significantly down-regulated at four different time points. Moreover, it dropped significantly in the fat body and hemolymph at 24 h after treatment. The bioassay results indicated that the mortality of L. migratoria manilensis treated with dsSerpin1 + Metarhizium was significantly higher than the other three treatments. Furthermore, the immune-related genes (PPAE, PPO, and defensin) treated by dsSerpin1 + Metarhizium were significantly down-regulated compared with the Metarhizium treatment, but the activities of phenoloxidase (PO), peroxidase (POD), superoxide dismutase (SOD), glutathione S-transferase (GST), and multifunctional oxidase (MFO) were fluctuating. Our results suggest that Lmserpin1 plays a crucial role in the innate immunity of L. migratoria manilensis. Lmserpin1 probably took part in regulation of melanization and promoted the synthesis of antimicrobial peptides (AMPs).
Highlights
Host and pathogens are an interactive relationship locked in a perpetual evolutionary marathon due to the evolving microorganisms and adaptable host immune system [1,2].Innate immunity is a fundamental self-protection system that evolved in all animals to protect against exogenous pathogenic signal
The results indicated that Lmserpin1 was consistently expressed in all life stages (Figure 1A), and its expression level increased with the development of L. migratoria manilensis, reaching peak at 3rd instars
When infected by M. anisopliae, we found that Lmserpin1 was expressed with a higher level at 6 h, 12 h, and 24 h after treatment, which means that Lmserpin1 gene was involved in the immune response of migratory locusts (Figure 3)
Summary
Host and pathogens are an interactive relationship locked in a perpetual evolutionary marathon due to the evolving microorganisms and adaptable host immune system [1,2]. Innate immunity is a fundamental self-protection system that evolved in all animals to protect against exogenous pathogenic signal. Insects rely solely on innate immune mediators to prevent infection [3,4]. Pathogen-associated molecular patterns (PAMPs) activate host cell-surface receptors (pathogen-recognition receptors or PRRs) when infection occurs. These signal cascades activate both cellular and humoral innate immune mechanisms [5,6,7]. Once insects are invaded by external microorganisms, prophenoloxidase-activating enzyme (PPAE) activate the prophenoloxidase cascade reaction (PPO cascade), and specific serine protease activate the phenoloxidase (PO)
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