Chromosomal locations of Populus CCCH genes. 90 CCCH genes are mapped to the 19 Linkage Groups (LG), while only one gene (PtC3H29) resides on unassembled scaffolds. The schematic diagram of Populus genome-wide chromosome organization arisen from the salicoid genome duplication event was adapted from Tuskan et al., (2006) . Segmental duplicated homologous blocks are indicated with the same color. Small boxes connected by colored line (two types) indicate corresponding sister gene pairs, of which the genes connected by solid line locate in the duplicated blocks, while one or both of genes connected by the dashed line was (were) not observed in the duplicated blocks. Tandemly duplicated genes are encompassed in the black boxes. Scale represents the length (4.84 Mb) of chromosome I.