Phylogenetic relationships, gene structure and motif compositions of Populus CCCH genes. A. Multiple alignments of 91 full-length CCCH proteins from Populus were conducted by Clustal X 1.83 and the phylogenetic tree was constructed using MEGA 4.0 by the Neighbor-Joining (NJ) method with 1,000 bootstrap replicates. The percentage bootstrap scores higher than 50 % are indicated on the nodes. The tree shows 13 major phylogenetic subfamilies (subfamily I to XIII marked with different color backgrounds) with high predictive value. B. Exon/intron organization of Populus CCCH genes. Green box represents exon and black line represents intron. The sizes of exons and introns can be estimated using the scale at bottom. C. Schematic representation of the conserved motifs in Populus CCCH proteins elucidated by SMART online. Each colored box represents a motif in the protein with motif name indicated in box on the right side. The length of the protein and motif can be estimated using the scale at bottom. Refer to Additional file 4 for details of individual motif.