Distribution of LRR-RLK genes on Populus chromosomes. Genes are mapped to LG according the Joint Genome Institute Poplar Genome version 2.0. The schematic diagram of Populus chromosome organization arisen from the salicoid genome duplication event was adapted from Tuskan et al., (2006) . Scale represents a 1 Mb chromosomal distance. Segmental duplicated homologous blocks are indicated with the same color and corresponding sister gene pairs were connected by colored lines. Tandemly duplicated genes are encompassed in the green boxes.