Since their discovery in Drosophila melanogaster, sPLA2s have been widely studied in insects. sPLA2s are a family of small secreted proteins (14–18 kDa) that typically have 5–8 disulfide bonds. In addition to iPLA2s, some sPLA2s have been characterized in different insects. These studies show that insect iPLA2 may play crucial biological roles in development and immunity. Otherwise, PLA2-VIA mutation in Drosophila caused increased sensitivity to oxidative stress, progressive neurodegeneration, and a severely reduced lifespan. IMD/Toll pathways have been shown to regulate these two i PLA2s, and immune challenges with different types of pathogens significantly increased their transcription. Insect iPLA2s, such as SeiPLA2A and SeiPLA2B, were first discovered in Spodoptera exigua, and have been demonstrated to play crucial physiological roles in insect immunity and larval growth. However, there is little research on iPLA2s in insects despite their relevance in various physiological processes. iPLA2 plays a key role in membrane remodeling, AAs release, secretion, and other processes in mammals, etc.
iPLA2s are Ca 2+-independent enzymes that range in molecular masses from 28 kDa to 146 kDa. Among PLA2, iPLA2s have only been found in a few insects. In living organisms, the PLA2 superfamily is divided into 16 groups, which were further classified into three types based on their properties: Ca 2+-dependent cellular PLA2 ( cPLA2), secretory PLA2 ( sPLA2), and Ca 2+-independent cellular PLA2 ( iPLA2). Our findings imply that BmiPLA2A and BmiPLA2B may have important biological roles in the development and innate immunity of B. Furthermore, challenged with virus, fungus, Gram-negative bacteria, and Gram-positive bacteria induced the expression of BmiPLA2A and BmiPLA2B with variable degrees along with different time points. The administration of 20-hydroxyecdysone increased their expression levels in the epidermis and hemocytes.
BmiPLA2A and BmiPLA2B were transcribed widely in various tissues and developmental stages with different expression patterns.
Domain analysis revealed that BmiPLA2A had six ankyrin repeat domains, but BmiPLA2B lacks these domains. In contrast, BmiPLA2B had a 1731 bp ORF that coded for a protein with 576 amino acids. BmiPLA2A had a 2427 base pair (bp) open reading frame (ORF) that coded for a protein with 808 amino acids. In this study, we identified two iPLA2 genes (designated as BmiPLA2A and BmiPLA2B) in the silkworm, Bombyx mori. In mammals, the biological roles of Ca 2+-independent Phospholipase A2 (iPLA2) have been extensively studied however, only a few studies have attempted to explore iPLA2 functions in insects. Phospholipase A2 (PLA2) catalyzes phospholipids, the initial step in eicosanoid biosynthesis.
Eicosanoids are crucial downstream signals in the insect immune responses.
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