Modification of lignin in crops via genetic engineering aims at reducing biomass recalcitrance to facilitate conversion processes. These improvements can be achieved via the expression of exogenous enzymes that interfere with biosynthetic pathways responsible for the production of the lignin precursors. In-planta expression of bacterial 3-dehydroshikimate dehydratase (QsuB) reduces lignin and alters its monomeric composition, which enables higher yields of fermentable sugars after cell wall polysaccharide hydrolysis. Understanding how crops respond to such genetic modifications at the transcriptional and metabolic levels is needed to facilitate further improvement and field deployment. In this work, we gathered some fundamental knowledge on lignin-modified QsuB poplar grown in a greenhouse using RNA-seq and metabolomics. The data showed that some changes in gene expression and metabolite abundance occur only in a specific tissue such as the xylem, phloem, or periderm. In the poplar line that exhibits the strongest reduction of lignin, we found that 3% of the transcripts had altered expression levels and ~19% of the detected metabolite ions had different abundances in the xylem from mature stems. Changes affect predominantly the shikimate and phenylpropanoid pathways as well as, secondary cell wall metabolism, and result in significant accumulation of hydroxybenzoates that derive from protocatechuate and salicylate.