Schematic view of the scattered distribution of the poplar MAPK genes (PtMPKs) over the Populus trichocarpa genome. Twelve of the 19 poplar chromosomes are presented as vertical bars. In addition, two scaffolds containing a PtMPK gene are shown. PtMPK genes are represented by colored boxes and the color code presented here is also used in the other figures. Recent duplication events between paralogous genes are indicated using dotted lines.