Abstract
Insect prophenoloxidases (PPOs) are a group of important innate immunity proteins and play an important role in melanin synthesis, defending the intruding microorganisms and parasites, healing wound and cuticle pigmentation. However, there is little study about immune-related defense mechanisms in Apis cerana cerana. Here we isolated a PPO gene from A. cerana cerana and evaluated the connection of AccPPO to immunity. AccPPO has an open reading frame of 2079 bp encoding a 693 amino acid protein. The genomic structure analysis showed that AccPPO is similar to that of AmPPO. AccPPO is also close to AmPPO in the evolutionary period. AccPPO expression could be detected in all the developmental stages of A. cerana cerana and was the highest in 15-day postemergence adults. In addition, we also found that AccPPO was induced by the infection of Ascosphaera apis and various oxidative stresses including 4, 16°C; UV light; and pesticides (acaricide, cyhalothrin, paraquat) treatments. These results revealed that AccPPO may play a critical role in resisting Ascosphaera apis and preventing A. cerana cerana from oxidative stresses.
Highlights
IntroductionCellular immunity is involved in circulating hemocytes that perform phagocytosis (of small bacteria) and encapsulation (around large parasites) [1]
Insect immunity is composed of cellular and humoral immunity
Based on the sequence information of PPO genes in Apis mellifera, Apis dorsata, Apis florae, Bombus impatiens, Megachile rotundata, the partial cDNA sequence of AccPPO was cloned using a combination of reverse transcription PCR (RT-PCR) and rapid amplification of cDNA ends (RACE)
Summary
Cellular immunity is involved in circulating hemocytes that perform phagocytosis (of small bacteria) and encapsulation (around large parasites) [1]. While humoral immunity is induced through immunity proteins in hemolymph [2]. Insects depend on their innate immune system to protect against invasion by pathogens or parasites [3,4]. Insect prophenoloxidases (PPOs) are a group of important innate immunity proteins and are the zymogen of phenoloxidases (POs), which are generated by PPOs when insects are injuried and invaded by microbial or parasite [5]. Activated phenoloxidase (PO) can catalyse the formation of melanin during bacteria and parasite infections and melanin can encase and kill the invading pathogens [2,6]. POs, which catalyse the hydroxylation of monophenol to o-diphenol and its oxidation to o-quinone and o-quinone can generate in a nonenzymatic reaction [7,8], function in melanin synthesis and are necessary for defense against intruding microorganisms and parasites, wound healing and cuticle pigmentation [9]
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