Molecular Evolution of Glycoside Hydrolase Genes in the Western Corn Rootworm (Diabrotica virgifera virgifera)

Abstract

Cellulose is an important nutritional resource for a number of insect herbivores. Digestion of cellulose and other polysaccharides in plant-based diets requires several types of enzymes including a number of glycoside hydrolase (GH) families. In a previous study, we showed that a single GH45 gene is present in the midgut tissue of the western corn rootworm, Diabrotica virgifera virgifera (Coleoptera: Chrysomelidae). However, the presence of multiple enzymes was also suggested by the lack of a significant biological response when the expression of the gene was silenced by RNA interference. In order to clarify the repertoire of cellulose-degrading enzymes and related GH family proteins in D. v. virgifera, we performed next-generation sequencing and assembled transcriptomes from the tissue of three different developmental stages (eggs, neonates, and third instar larvae). Results of this study revealed the presence of seventy-eight genes that potentially encode GH enzymes belonging to eight families (GH45, GH48, GH28, GH16, GH31, GH27, GH5, and GH1). The numbers of GH45 and GH28 genes identified in D. v. virgifera are among the largest in insects where these genes have been identified. Three GH family genes (GH45, GH48, and GH28) are found almost exclusively in two coleopteran superfamilies (Chrysomeloidea and Curculionoidea) among insects, indicating the possibility of their acquisitions by horizontal gene transfer rather than simple vertical transmission from ancestral lineages of insects. Acquisition of GH genes by horizontal gene transfers and subsequent lineage-specific GH gene expansion appear to have played important roles for phytophagous beetles in specializing on particular groups of host plants and in the case of D. v. virgifera, its close association with maize.

Genome of the Asian longhorned beetle (Anoplophora glabripennis), a globally significant invasive species, reveals key functional and evolutionary innovations at the beetle–plant interface

“…GH5 subfamily 2 genes were likely acquired via HGT from Bacteroidetes [27]. GH45 genes were likely acquired by the last common ancestor (LCA) of the Phytophaga (the sister beetle superfamilies Chrysomeloidea and Curculionoidea) via HGT from a fungus [28, 29]. Amino acid sequences of beetle GH48 cellulases are similar to bacterial cellobiosidases, but their function(s) remain unclear; they may have evolved to scavenge nitrogen by degrading chitin in the gut or diet [81], e.g., from host plant tissues containing fungi, or from fungi resident in the gut (e.g., yeasts, Fusarium solani ) which are thought to concentrate nitrogen and synthesize essential amino acids [9, 30, 35].…”

Differential expression of endogenous plant cell wall degrading enzyme genes in the stick insect (Phasmatodea) midgut

“…Phasmid endoglucanases are of the GH9 family thought to be ancestral to all animal life [21], as opposed to the GH5, 45, or 48 cellulases found in nematodes and beetles [23]. The phasmid transcripts either themselves included or were homologous to transcripts including the known active sites invariant in GH9 cellulases, based on work on Thermobifida/Thermomonospora fusca (PDB: 1js4) [56, 57]: namely two conserved Asp’s (D55, D58) functioning in catalytic base activity and a Glu residue (E461) that functions as the catalytic acid (Figure 3).…”

Developing an in vivo toxicity assay for RNAi risk assessment in honey bees, Apis mellifera L

“…The D. v. virgifera vATPase-A sequence was obtained from a de novo transcriptome assembly of cDNA prepared from eggs, neonates and midguts of third instar larvae (Eyun et al, 2014). D. v. virgifera vATPase-A sequence has been deposited in GenBank, accession number KR024028, and A. mellifera vATPase-A sequence was obtained from the GenBank, accession number XM_623492.4.…”