Transcriptional identification of differentially expressed genes during the prepupal-pupal transition in the oriental armyworm, Mythimna separata (Walker) (Lepidoptera: Noctuidae)

Expressions and functions of RR-1 cuticular protein genes in the integument of Mythimna separata

As the most outer layer between itself and the environment, integuments are necessary for insects with various important functions. Cuticular proteins (CPs) are the main components in integuments, while the functions of CP genes remain unknown in Mythimna separata (Walker), which is a devastating agricultural pest. In this study, 79 CP genes were identified from the transcriptomes of larval integuments, 57 of which were from the family containing conserved Rebers & Riddiford (R&R) consensus (CPR family). Amongst these CPRs, 44 genes belonged to the subfamily with RR-1 motif (RR-1 genes) and clustered into three clades, with the top 15 most abundant RR-1 genes identified based on fragments per kilobase per million mapped fragments (FPKM) values. RT-qPCR analysis showed that most of RR-1 genes such as MsCPR1-4 were highly expressed at larval stages and in their integuments. The expression levels of RR-1 genes were generally decreased at the beginning but increased at the late stage of molting process. RNAi was applied for six RR-1 genes, and MsCPR1-4 were knocked down significantly. Silence of MsCPR2 resulted in abnormal integument formed after molting, while knockdown of MsCPR3 and MsCPR4 led to failure of molting, respectively. No phenotype was obtained for the RNAi of MsCPR1. Therefore, the expression of RR-1 genes and their functions were analyzed in the development of integuments in M. separata, providing new insights of RR-1 genes and potential targets for the development of growth regulators and new insecticides for M. separata.

Integrated Analysis of Transcriptome and Proteome to Reveal Pupal Color Switch in Papilio xuthus Butterflies

Pupal color polyphenism in Papilio butterflies, including green, intermediate, or brown, is an excellent study system for understanding phenotypic plasticity. Previous studies suggested that development of brown pupae may be controlled by a hormone called pupal-cuticle-melanizing-hormone (PCMH) which is synthesized and secreted from brain-suboesophageal ganglion and prothoracic ganglion complexes (Br-SG-TG1) during the pre-pupa stage. However, detailed molecular mechanisms of neuroendocrine regulation in pupal color development remain unknown. In this study, we integrated the expression profiles of transcriptome and proteome at pre-pupa stages [2 h after gut purge (T1) and 3 h after forming the garter around the body (T2)] and pigmentation stages [10 h after ecdysis (T3) and 24 h after ecdysis (T4)] to identify important genes and pathways underlying the development of green and brown pupa in the swallowtail butterfly Papilio xuthus. Combined comparisons of each developmental stage and each tissue under green and brown conditions, a total of 1042 differentially expressed genes (DEGs) and 430 different abundance proteins (DAPs) were identified. Weighted gene co-expression network analysis (WGCNA) and enrichment analysis indicate that these DEGs were mainly related to oxidation-reduction, structural constituent of cuticle, and pigment binding. Soft clustering by Mfuzz and enrichment analysis indicate that these DAPs are mainly involved in tyrosine metabolism, insect hormone biosynthesis, and melanogenesis. By homologous alignment, we further identified those genes encoding neuropeptides (51), GPCRs (116), G-proteins (8), cuticular proteins (226), chitinases (16), and chitin deacetylases (8) in the whole genome of P. xuthus and analyzed their expression profiles. Although we identified no gene satisfying with hypothesized expression profile of PCMH, we found some genes in the neuropeptide cascade showed differentially expressed under two pupal color conditions. We also found that Toll signaling pathway genes, juvenile hormone (JH) related genes, and multiple cuticular proteins play important roles in the formation of selective pupal colors during the prepupal-pupal transition. Our data also suggest that both green and brown pupa include complex pigment system that is regulated by genes involved in black, blue, and yellow pigments. Our results provide important insights into the evolution of pupal protective colors among swallowtail butterflies.