Fig. 1

Insect feeding causes conserved up-regulation of gene expression across eight elite poplar clones. a Principal component analysis (PCA) shows clustering of RNA-seq samples by treatment and species. While PC1, explaining 38% of the total variance, separates treated samples from control samples, PC2, explaining 23% of the total variance, differentiates pure P. trichocarpa clones (blue) from the hybrids P. maximowiczii x P. trichocarpa (red) and P. nigra x P. maximowiczii (yellow). b Volcano plot showing the 23,907 expressed genes. Significantly differentially expressed genes in response to insect feeding (adjusted P < 0.01 and absolute log2 fold change > 1.5) are depicted in red. While 885 genes are up-regulated, only 92 genes exhibit down-regulation under herbivory. The size of the dots corresponds to the p-value. The dashed line indicates the p-value significance threshold