A chromosome-level genome assembly and intestinal transcriptome of Trypoxylus dichotomus (Coleoptera: Scarabaeidae) to understand its lignocellulose digestion ability

Lignocellulose, as the key structural component of plant biomass, is of recalcitrant structure and is difficult to degrade. Meanwhile, the improper handling of plant residues is accelerating the process of global warming. Interestingly, we noticed that the xylophagous beetle, Trypoxylus dichotomus has a significant ability to decompose lignocellulosic biomass. However, no study has been conducted to elucidate the digestion mechanism from a genome-wide aspect for this beetle. Based on sequencing and assembling, the draft genome size of T. dichotomus is 636.27 Mb, with 95.37% scaffolds anchored onto 10 chromosomes. The phylogenetic results indicated that T. dichotomus and its closely related scarabaeid species Onthophagus taurus split from each other in the early Cretaceous. Furthermore, two digestive gene families (Trypsin and Enoyl-(Acyl carrier protein) reductase) have experienced significant expansion, accounting for the high degradation efficiency of lignocellulose. Additionally, the collinearity analysis revealed that chromosome breakages and rearrangements occur in the evolution of T. dichotomus due to chromosomes 6 and 8 of T. dichotomus being intersected with chromosomes 2 and 10 of Tribolium castaneum respectively. As suggested by the larval intestinal transcriptome comparative analyses, the digestive ability of midgut is much stronger than that of hindgut, even though susceptible to different food habits. This study reported the well-assembled and annotated genome of this rhinoceros beetle, providing genomic and transcriptomic bases for further understanding the functional mechanism and evolutionary history of lignocellulolytic digestion of the beetle.