Transglutaminase (TGase) regulates encapsulation response of the Oriental Armyworm, <i>Mythimna separata</i> (Lepidoptera: Noctuidae)

Transglutaminase (TGase) is a Ca²⁺-dependent acyltransferase that catalyzes protein cross-linking. We previously reported that the TGases of Mythimna separata, that is, MysTGase1 and MysTGase2, contribute to insect immune responses against microbial invaders. In this study, we aimed to elucidate the involvement of MysTGases in the encapsulation immune responses that target large invaders such as parasitoid eggs and nematodes. The expression levels of mystgases in hemocytes forming capsules around beads and nematodes were significantly higher than those in circulating hemocytes and increased in a size-dependent manner with increasing bead size. The expression of both mystgases was detected in plasmatocytes and granulocytes, which are the capsule components. RNA interference targeting mystgase1 or mystgase2 led to a significant decrease in the encapsulation rate of the beads, whereas treatment with recombinant MysTGases had the opposite effect. Furthermore, the knockdown of mystgase2 inhibited plasmatocyte spreading, whereas mystgase1 did not. This study highlights the potential significance of TGase in the encapsulation process and presents a notable molecular discovery of the encapsulation mechanism. This study also provides a scientific foundation for future research on insect immunity and may contribute to the development of innovative pest control strategies.