Variation of insulin-related peptides accompanying the differentiation of Aphis gossypii biotypes and their expression profiles

Abstract

Insulin signaling plays a critical role in regulating various aspects of insect biology, including development, reproduction, and the formation of wing polyphenism. This leads to differentiation among insect populations at different levels. The insulin family exhibits functional variation, resulting in diverse functional pathways. Aphis gossypii Glover, commonly known as the cotton-melon aphid, is a highly adaptable aphid species that has evolved into multiple biotypes. To understand the genetic structure of the insulin family and its evolutionary diversification and expression patterns in A. gossypii, we conducted studies using genome annotation files and RNA-sequencing data. Consequently, we identified 11 insulin receptor protein (IRP) genes in the genomes of the examined biotypes. Among these, eight AgosIRPs were dispersed across the X chromosome, while two were found in tandem on the A1 chromosome. Notably, AgosIRP2 exhibited alternative splicing, resulting in the formation of two isoforms. The AgosIRP genes displayed a high degree of conservation between Hap1 and Hap3, although some variations were observed between their genomes. For instance, a transposon was present in the coding regions of AgosIRP3 and AgosIRP9 in the Hap3 genome but not in the Hap1 genome. RNA-sequencing data revealed that four AgosIRPs were expressed ubiquitously across different morphs of A. gossypii, while others showed specific expression patterns in adult gynopara and adult males. Furthermore, the expression levels of most AgosIRPs decreased upon treatment with the pesticide acetamiprid. These findings demonstrate the evolutionary diversification of AgosIRPs between the genomes of the two biotypes and provide insights into their expression profiles across different morphs, developmental stages, and biotypes. Overall, this study contributes valuable information for investigating aphid genome evolution and the functions of insulin receptor proteins.

Keywords: RNA‐sequencing; aphid; gene variation; genome; population evolution; transposon.

FIGURE 1

Schematic of the AgosIRPs located on Aphis gossypii chromosomes.

FIGURE 2

Predicted structure and gene variation of IRPs between aphids. Sequence names are indicated by a prefix formed from the abbreviated species name (Aphis craccivora, Acra; Aphis glycines, Agly; Acyrthosiphon pisum, Apis; Daktulosphaira vitifoliae, Dv; Diuraphis noxia, Dnox; Melanaphis sacchari, Msac; Myzus persicae, Mper; and Rhopalosiphum maidis, Rmai), followed by the IRP protein sequences accession number.

FIGURE 3

Phylogenetic tree based on nuclear acid sequences of IRP transcripts from various aphid species. IRP transcripts sequence was aligned with MAFFT v7.505 using “‐‐auto” strategy and codon alignment mode. Gap sites were removed with trimAI v1.2rev57 using “‐automated1” command. ModelFinder v2.2.0 was used to select the best‐fit model using BIC criterion. Maximum likelihood phylogenies were inferred using IQ‐TREE v2.2.0 under the model automatically selected by IQ‐TREE (“Auto” option in IQ‐TREE) for 20,000 ultrafast bootstraps, as well as the Shimodaira–Hasegawa–like approximate likelihood‐ratio test. The IRPs from different species are highlighted by various colors. The labels include the species name and the corresponding IRP transcript accession number.

FIGURE 4

Predicted structure and gene variation of AgosIRPs between Hap1 and Hap3. (a) AgosIRP2 exists in one alternative splicing site in ORF region, and is present in two isoforms (AgosIRP2a and AgosIRP2b); amino acid different between Hap1 and Hap3 of AgosIRP3 (b) and AgosIRP9 (c). Disulfide bonds between conserved cysteines are indicated by yellow color; the black dot below the sequence indicates the signal peptide; the solid black line below the sequence indicates the A chain or B chain; and black five‐pointed star denote canonical prohormone convertase or furin cleavage sites.

FIGURE 5

Mapped RNA‐seq reads were used to show novel mRNA alternative splicing in AgosIRP2.

FIGURE 6

Relative expression quantity of AgosIRPs in polymorphism Aphis gossypii. AgosIRP2 in four morphs of A. gossypii adult aphid (including alate parthenogenetic females, apterous parthenogenetic females, gynoparae, and male) (a), different development stages of male (b), biotypes Hap1 and Hap3 (c); AgosIRP3 in four morphs of A. gossypii adult aphid (including alate parthenogenetic females, apterous parthenogenetic females, gynoparae, and male) (d), different development stages of male (e), biotypes Hap1 and Hap3 (f); AgosIRP6 in four morphs of A. gossypii adult aphid (including alate parthenogenetic females, apterous parthenogenetic females, gynoparae, and male) (g), different development stages of male (h), biotypes Hap1 and Hap3 (i); AgosIRP7 in four morphs of A. gossypii adult aphid (including alate parthenogenetic females, apterous parthenogenetic females, gynoparae, and male) (j), different development stages of male (k), biotypes Hap1 and Hap3 (l). First instar nymph male (male‐N1), second instar nymph male (male‐N2), third instar nymph male (male‐N3), fourth instar nymph male (male‐N4), and adult male (male‐A). The Y‐axis was the transcript per million (TPM) value (mean ± standard error of the mean). Different lowercase letters (a–d) indicate significant differences between treatments (p < .05) according to the post hoc Tukey's HSD method; *p < .05, ns, no significant difference, data were analyzed by Mann–Whitney U test.

FIGURE 7

Relative expression quantity of AgosIRPs in Aphis gossypii treated with pesticide acetamiprid. (a): AgosIRP2; (b): AgosIRP3; (c): AgosIRP6; (d): AgosIRP7. The Y‐axis was the transcript per million (TPM) value (mean ± standard error of the mean). NS and MS were two susceptible clones, KR was one resistant clone, (T) means with acetamiprid treatment (Hirata et al., 2017). *p < .05, ns, no significant difference, data were analyzed by Mann–Whitney U test.