The NF-YB7 gene of P. nigra × (P. deltoides × P. nigra). (A) Multiple alignment of amino acid sequences of PdNF-YB7 and other plant NF-YBs. AtNF-YB1 (AT2G38880), AtNF-YB2 (AT5G47640), and AtNF-YB3 (AT4G14540) sequences were obtained from the TAIR database and ZmNF-YB2 (DQ333305), PeNF-YB7 (HQ161880), and PtNF-YB7 (POPTR_0007s06480) from NCBI and PopGenIE. The helix motifs are underlined in black (α1, α2, α3, and αC) and the loops are between two helixes (L1, L2, and L3). The Arg and Asp residues, highlighted in red, function in the combination of NF-YB and NF-YC. The two Glu residues, highlighted in yellow, function in the junction with NF-YA. (B) Phylogenetic relationships between poplar and Arabidopsis NF-YB family members. The Phylogeny.fr online web service was used for analysis of phylogenetic relationships. The Arabidopsis NF-YB family sequences were obtained from the TAIR database and the poplar NF-YB family sequences from the PopGenIE database.