Phaedon cochleariae RNAi knockdown of GH28

A large diversity of protein families harbour pseudoenzymes that lost the catalytic function of their enzymatically active counterparts. But assigning alternative function and importance to these proteins is challenging (10.1042/BST20160400). The evolution towards pseudoenzymes is driven by gene duplication and thus they often accumulate in multigene families. Plant cell wall degrading enzymes (PCWDE) are prominent examples of expanded gene families. The pectolytic glycoside hydrolase family 28 (GH28) allows herbivorous insects to crack the PCW polysaccharide pectin. GH28 in the Phytophaga clade of beetles contain many active enzymes but also a large number of inactive counterparts. By functional characterization, gene silencing, global transcriptome analyses and life history trait recordings, we found that not only catalytically active but also inactive GH28 proteins are part of the same – pectin digesting – pathway. Robustness and plasticity of this pathway and thus its importance for the beetle is supported by extremely high steady state expression levels and counter-regulatory mechanisms. Unexpectedly, the impact of pseudoenzymes on the pectin digesting pathway in Phytophaga beetles even exceeds the one of their active counterparts.