Chromosome-level genome assembly and transcriptomes of the leaf insect Cryptophyllium westwoodii provide insights into the evolution of leaf-like masquerade.

backgroundLeaf insects in the family Phylliidae are regarded as nature's ultimate masqueraders, evolving the leaf-resembling morphology to avoid predation. However, the lack of a high-quality reference genome for the leaf insects has hindered the exploration of the genetic mechanisms of leaf-like masquerade in insects.

resultsWe generated a chromosome-level genome assembly of Cryptophyllium westwoodii using Nanopore and Hi-C sequencing. 98.3% of the 4.12 Gb assembly (scaffold N50 = 256.9 Mb, 98.6% BUSCO completeness) was anchored onto 15 pseudo-chromosomes, including 13 autosomes, an X chromosome, and a putative B chromosome. Genome annotation predicted a total of 2.29 Gb repetitive sequences and 19,131 protein-coding genes. The chromosomal collinearity analysis indicated that many homologous gene fragments were detected between B chromosome and the other 14 A chromosomes in C. westwoodii, suggesting the B chromosome could have a mosaic origin based on homologous gene fragments from A chromosomes. Comparative genomic and transcriptomic analyses indicated that resilin gene with 24 copies expanded in C. westwoodii, of which 10 copies showed significantly different expression in the laterally leaf-like abdominal expansions at five developmental stages. These findings suggest that Cuticle genes, particularly resilin, may contribute to the leaf masquerade morphology in C. westwoodii, implying their possible role in the evolution of this adaptive trait.

conclusionsThis study not only provides the first chromosome-level reference genome of leaf insects in Phylliidae, but also offers new insights into the leaf-like masquerade in leaf insects.