Chromosomal locations of Populus NAC genes. Only 120 NAC genes are mapped to the 19 Linkage Groups (LG), while the other 43 genes reside on unassembled scaffolds. The schematic diagram of genome-wide chromosome organization arisen from the salicoid genome duplication event in Populus was adapted from Tuskan et al., (2006) . Segmental duplicated homeologous blocks are indicated with the same color. Only the duplicated regions containing NAC genes are connected with lines in shaded colors. Tandemly duplicated genes are indicated with red lines. Scale represents a 5 Mb chromosomal distance.