library_construction_protocol: Leaves/roots were cut off and directly frozen in liquid nitrogen. Poplar plants were micro-propagated in ½ MS and grown for 14 days. At day 0 of the experiment, the poplar plants were transferred on top of ½ MS in squared petri dishes. Dishes were placed vertically in the culture room and grown under long day conditions (16 h light, 60-85 µE/ 8 h dark) at 22 °C. Humidity was kept between 40-60 %. L. bicolor was grown from culture on cellophane and P20 medium for 14 days at 22 °C in darkness. Per bi-compartmented squared Petri dish, 1 14-days-old P. canescens plantlet was co-incubated with 4 14-days-old L. bicolor plugs. Control plantlets were grown with cellophane and P20. After 2 and 7 days of co-incubation, roots and leaves were harvested. Poplar root RNA was extracted according to CTAB extraction protocol (Chang et al., 1993). Poplar leaf RNA was extracted using the innuPREP Plant RNA Kit (Anayltik Jena, Jena, Germany). Poly-A RNA was enriched using the NEBNext Poly (A) mRNA Magnetic Isolation Module (New England Biolabs (NEB), Ipswich, Massachusetts, USA). Sequencing libraries were prepared using the NEBNext Ultra RNA Library Prep Kit for Illumina (NEB) according to manufacturer's instructions.