A transcriptional roadmap of the yearly growth cycle in Populus trees

Populus species are widely spread over all the boreal hemisphere and have adapted to a to a broad range of environments. In these regions the climate is characterized by distinctly contrasting seasons, where the environmental conditions vary considerably. It is indeed the alteration of these conditions, like daylength and temperature, which trigger a molecular response in trees, regulating crucial developmental and phenological processes. Even though these processes are crucial for the trees' growth and reproduction, little is known about the genes involved. We performed RNA sequencing on 208 samples collected from several tissues in multiple environmental conditions, indoors and outdoors, to generate a complete transcriptional roadmap of the yearly growth cycle of Populus trees. Co-expression network analyses generated 46 modules. The heatmaps of 36 of these modules show a seasonal expression profile in both outdoor and indoor samples. The module networks illustrate the genes hubs involved in each molecular process specific to each season and phenological change of Populus trees during the year. To make the dataset simple and accessible to everyone we created an R package “Shiny” application: POPUL-R (link). Through POPUL-R, users can visualize expression data for one or multiple genes and create interactive networks. The app's multiple features make it a very valuable tool for the scientific community to explore the role of specific genes in the annual growth cycle of Populus trees.