Comprehensive transcriptomic analysis reveals detoxification gene expansion and adaptive genetic variation in the...

The bark beetle Acanthotomicus suncei is an emerging destructive pest of the introduced American sweetgum (Liquidambar styraciflua) in China. The molecular mechanisms underlying its successful adaptation to this exotic host, particularly its ability to overcome plant chemical defenses, remain largely unknown. We conducted a comprehensive transcriptomic analysis of A. suncei. Our assembly yielded 30,557 unigenes (N50 = 2175 bp). We identified a significant expansion of genes within three major detoxification enzyme families: 122 cytochrome P450 monooxygenases (P450s), 75 carboxylesterases (COEs), and 47 glutathione S-transferases (GSTs). This repertoire is notably larger than that of many compared curculionid beetles. Phylogenetic analyses revealed complex evolutionary relationships, with A. suncei clustering closely with Dendroctonus species in some P450 and GST clades, while showing considerable divergence in others. Furthermore, we uncovered abundant genetic variation, with single nucleotide polymorphisms (SNPs) being highly prevalent within the coding sequences of these detoxification genes, especially P450s. Simple sequence repeat (SSR) analysis indicated a predominance of A/T-rich motifs. The remarkable expansion and substantial genetic variation observed in the detoxification gene families of A. suncei provide a compelling molecular basis for its potent detoxification capacity. These findings suggest that an enriched and highly adaptable detoxification system likely facilitates this beetle's successful colonization of the exotic host L. styraciflua. This study offers crucial insights into the molecular mechanisms of host adaptation in an emerging forest pest and identifies potential genetic targets for future management strategies.