Multifunctional cellulase enzymes are ancestral in Polyneoptera

Many hemimetabolous insects produce their own cellulase enzymes from the glycoside hydrolase family 9, first observed in termites and cockroaches. Phasmatodea have multiple cellulases, some of which are multifunctional and can degrade xylan or xyloglucan. To discover when these abilities evolved, we identified cellulases from the Polyneoptera sampled by the 1000 Insect Transcriptome and Evolution (1KITE) project, including all cockroach and termite transcriptomes. We hoped to identify what role enzyme substrate specificities had in the evolution of dietary specification, such as leaf-feeding or wood-feeding. Putative cellulases were identified from the transcriptomes and analysed phylogenetically. All cellulases were amplified from an exemplar set of Polyneoptera species using rapid amplification of cDNA ends PCR and heterologously expressed in an insect cell line, then tested against different polysaccharides for their digestive abilities. We identified several multifunctional xyloglucanolytic enzymes across Polyneoptera, plus a large group of cellulase-like enzymes found in nearly all insect orders with no discernible digestive ability. Multifunctional xylanolytic cellulases remain unique to Phasmatodea. The presence or absence of multifunctional enzymes does not impact dietary specification, but rather having multiple, multifunctional cellulase genes is an ancestral state for Polyneoptera and possibly Insecta. The prevalence of multifunctional cellulases in other animals demands further investigation.