Chemical and physical wood properties (e.g. cellulose/lignin content, density, stiffness) are complex genetic traits regulated by multiple genes. Unraveling gene interactions that control these traits would offer marker genes that can be used as prognostic tools in tree breeding. In this project, we aim to decipher gene interactions and genetic markers for economically important chemical and physical wood properties in Swedish aspen (Populus tremula, grown in Ekebo, harevsted 01-03.07.2019). For this purpose we obtained RNA-Seq data from developing/expanding xylem tissue from 298 aspen clones. Comparative expression analysis will reveal differentially regulated genes, expression quantitative trait loci (eQTL) and gene interactions that arise as consequence of genetic diversity and contribute to natural variation in wood properties. All information gained from genomic, transcriptomic and biochemical studies will be combined by a network-based data integration method.