It has been reported that a high population density alters insect prophylactic immunity. Bursicon plays a key role in the prophylactic immunity of newly emerged adults. In this paper, full-length cDNAs encoding the alpha and beta subunits of bursicon in Mythimna separata larvae (Msburs α and Msburs β) were identified. The cDNAs of Msburs α and Msburs β contain open reading frames (ORFs) encoding 145- and 139-amino acid residue proteins, respectively. Multiple alignment sequences and phylogenetic analysis indicated that Msbursicons (Msburs α and Msburs β) are orthologous to bursicons in other lepidopterans. The Msbursicons were expressed throughout all developmental states with higher relative expression during the egg, pupae, and adult stages. Msbursicons (Msburs α and Msburs β) were highly expressed in the ventral nerve cord and brain relative to other tested tissues. Msbursicon expression of larvae subject to high-density treatment (10 larvae per jar) was significantly increased compared with that of the larvae subject to low-density treatment (1 larva per jar) in the whole fourth and fifth instar stages. The trend in the expression of the antimicrobial peptide (AMP) genes cecropin C and defensin in the test stage was accorded and delayed with increased expression of bursicons. Silencing Msburs α (or Msburs β) expression by dsRNA injection in larvae subject to high-density treatment significantly decreased the expression levels of the cecropin C and defensin genes. Recombinant Msbursicon homodimers significantly induced the expression of the cecropin C and defensin genes. There was a notable decrease in the survival rate of the Msburs α (or Msburs β or Mscecropin C or Msdefensin) knockdown larvae infected by Beauveria thuringiensis. Our findings provide the first insights into how larval density mediates AMP gene expression, which subsequently affects the prophylactic immunity of insects under high-density conditions.

据报道，高人口密度会改变昆虫的预防性免疫。Bursicon 在新出现的成年人的预防性免疫中起关键作用。本文鉴定了分离Mythimna separata幼虫（Msburs α和Msburs β）中滑囊菌α和β 亚基的全长cDNA 。Msburs α和Msburs β的 cDNA包含分别编码 145 个和 139 个氨基酸残基蛋白的开放阅读框 (ORF)。多重比对序列和系统发育分析表明，Msbursicons（Msburs α和Msburs β）与其他鳞翅目动物的bursicons直系同源。这Msbursicons在所有发育状态中都有表达，在卵、蛹和成虫阶段具有较高的相对表达。Msbursicons ( Msburs α和Msburs β ) 在腹神经索和大脑中相对于其他测试组织高度表达。与低密度处理（每罐1只）的幼虫相比，高密度处理（每罐10只幼虫）的Msbursicon表达在整个第四和第五龄阶段显着增加。抗菌肽（AMP）基因天蚕素C和防御素在测试阶段的表达趋势与bursicons表达的增加一致并延迟。沉默Msburs α（或Msburs β）通过 dsRNA 注射在经受高密度处理的幼虫中表达显着降低了 cecropin C 和防御素基因的表达水平。重组Msbursicon同源二聚体显着诱导天蚕素 C 和防御素基因的表达。苏云金白僵菌感染的Msburs α（或Msburs β或Mscecropin C或Msdefensin）敲低幼虫的存活率显着下降。我们的研究结果首次揭示了幼虫密度如何介导 AMP 基因表达，从而影响昆虫在高密度条件下的预防性免疫。