Fig. 2.

Cellulase genes diversified in the Pristionchus lineage from a single horizontal transfer event. (A) Gene tree and domain compositions of eight cellulases in the model organism Pristionchus pacificus (wild-type strain PS312). The bootstrap value is 100 for all branches. The omega (ω) values are determined by branch models in PAML, which assumes independent ω values between cel-1 to cel-3 and cel-4 to cel-7. (B) Expression levels of cellulase genes in P. pacificus from a stage-specific RNA-seq data set. Total transcripts per million (TPM) from all stages (second to fourth juvenile and young adult) are shown. Red dots indicate the TPM in the young adult stage. (C) Horizontally acquired cellulase in eight Pristionchus species with available whole-genome sequence drafts. (Left) A phylogenetic tree of the Pristionchus species, the closely related species Micoletzkya japonica and C aenorhabditis elegans based on 1:1 orthologous genes from all species. (Right) Using a cellulase phylogenetic tree from the above species (supplementary fig. S3B, Supplementary Material online), cellulases are classified into six clusters with copy numbers of cellulase in each cluster being presented. A warmer color indicates a larger number of genes. Note that “ungrouped” cellulase genes are diverged sequences and do not support clustering. C aenorhabditis elegans does not have cellulase genes (shown as N/A).