250 Million Years of Convergent Evolution and Functional Divergence of Glycoside Hydrolase Family 28 Genes in Xylophagous Beetles (Cerambycidae and Buprestidae): Insights Into Horizontal Gene Transfer, Gene Dynamics, Synteny and Adaptive Divergence

Wood-feeding beetles harbour diverse gene families involved in plant cell wall degradation, including glycoside hydrolase family 28 (GH28) genes, which function as polygalacturonases. These genes are believed to have originated from microbial donors via horizontal gene transfers (HGT), followed by gene duplications. However, the evolutionary history of GH28 genes across independently evolved wood-feeding beetle lineages remains unclear. Here, we investigate the distribution, origin and diversification of GH28 genes in two xylophagous beetle groups, Cerambycidae: Lamiinae and Buprestidae: Agrilinae, which diverged over 250 million years ago. Phylogenetic analyses reveal that both groups possess GH28 genes most likely derived from ascomycete fungi, which are distinct from the 'ancestral-type' GH28 genes found in other Cerambycidae. Thus, Lamiinae and Agrilinae acquired similar 'new-type' GH28 genes via convergent HGT events. Comparative genomic analyses show conserved synteny around GH28 loci within each beetle subfamily, but not between them, consistent with independent acquisitions and endogenous retention. Subsequent lineage-specific duplications resulted in the expansion of GH28 gene copies, with protein structural modelling revealing divergent active sites and substrate-binding regions, suggesting functional differentiation and adaptation to distinct ecological contexts. Signatures of positive selection further support adaptive evolution of GH28 enzymes in both groups. Our findings demonstrate convergent acquisition and diversification of GH28 genes in distantly related xylophagous beetles, highlighting the roles of HGT, gene duplication and structural divergence in driving functional innovation. These results underscore how plant cell wall-degrading enzymes have contributed to trophic specialisation and the evolutionary success of specialised phytophagous beetles.