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. 2022 Jul 30;23(15):8444.
doi: 10.3390/ijms23158444.

Identification of the Gene Repertoire of the IMD Pathway and Expression of Antimicrobial Peptide Genes in Several Tissues and Hemolymph of the Cockroach Blattella germanica

Leo Zuber  1 , Rebeca Domínguez-Santos  1 , Carlos García-Ferris  1   2 , Francisco J Silva  1   3
Affiliations

Identification of the Gene Repertoire of the IMD Pathway and Expression of Antimicrobial Peptide Genes in Several Tissues and Hemolymph of the Cockroach Blattella germanica

Leo Zuber et al. Int J Mol Sci. .

Abstract

Antimicrobial peptide (AMP) genes, triggered by Toll and IMD pathways, are essential components of the innate immune system in the German cockroach Blattella germanica. Besides their role in killing pathogenic bacteria, AMPs could be involved in controlling its symbiotic systems (endosymbiont and microbiota). We found that the IMD pathway was active in the adult female transcriptomes of six tissues (salivary glands, foregut, midgut, hindgut, Malpighian tubules and fat body) and hemolymph. Total expression of AMP genes was high in hemolymph and salivary glands and much lower in the other sample types. The expression of specific AMP genes was very heterogeneous among sample types. Two genes, defensin_g10 and drosomycin_g5, displayed relevant expression in the seven sample types, although higher in hemolymph. Other genes only displayed high expression in one tissue. Almost no expression of attacin-like and blattellicin genes was observed in any sample type, although some of them were among the genes with the highest expression in adult female whole bodies. The expression of AMP genes in salivary glands could help control pathogens ingested with food and even determine gut microbiota composition. The low expression levels in midgut and hindgut are probably related to the presence of beneficial microbiota. Furthermore, a reduction in the expression of AMP genes in fat body could be the way to prevent damage to the population of the endosymbiont Blattabacterium cuenoti within bacteriocytes.

Keywords: Blattella germanica; IMD pathway; antimicrobial peptides (AMPs); innate immune response; symbiosis; transcriptome.

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Conflict of interest statement

The authors declare no conflict of interest.

Figures

Figure 1
Figure 1
Expression of genes of the IMD pathway in adult females of B. germanica. Values are the means plus standard deviations of normalized expression (GeTMM) of each gene in each sample type. Graph bars are standard deviations. See Table 1 for product names. Y-axis is in log scale. The lower ends of the error bars are not shown below 100. Genes are arranged in alphabetical order from left to right and top to bottom.
Figure 2
Figure 2
Total normalized expression (GeTMM) of AMP genes in seven sample types of B. germanica. Values are the means of expression of all AMP genes in each sample type. Graph bars are standard deviations. Abbreviations: FB (fat body), FG (foregut), HG (hindgut), HL (hemolymph), MG (midgut), MT (Malpighian tubules) and SG (salivary glands). Y-axis is in log scale.
Figure 3
Figure 3
Gene expression of AMP genes in seven sample types and whole bodies of B. germanica. Heatmap analysis of normalized expression (GeTMM) of AMP genes. Genes with identical CDS were grouped. The levels of expression in whole bodies (WB) are the means of three female adult SRA projects (SRR5458592.1, SRR5458593.1 and SRR6784711.1). See Figure 2 for abbreviations of sample types. GeTMM values < 1 are in white.
Figure 4
Figure 4
Normalized expression (GeTMM) of defensin and drosomycin genes in hemolymph and salivary glands of B. germanica. Values are the means plus standard deviations of gene expression of each sample type. Graph bars are standard deviations. Code colors are pink (hemolymph) and blue (salivary glands). Attacins, blattellicins and termicins are not shown because of their very low mean values. Y-axis is in log scale. The lower ends of the error bars are not shown below 100. All expressed genes, except defensin_g1 and defensin_g2, show a differential expression between the two sample types (|log2FoldChange| > 2). Differential expression was significant (adjusted p-value < 0.001) except for defensin_g7, defensin_g8 and drosomycin_g9.
Figure 5
Figure 5
Expression of AMP genes in fat body of B. germanica. Means and standard deviations of normalized expression (GeTMM) of AMP genes. Graph bars are standard deviations. Y-axis is in log scale. The lower ends of the error bars are not shown below 100. Color codes for gene families are: attacin-like (gray), blattellicin (pink), drosomycin (cyan), defensin (green) and termicin (violet).
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