Figure 9

Evolution scenario of the AHL gene family in land plants. In prokaryotes and picoeukaryotes, the PPC domain exists by itself as a PPC protein. The AHL gene family emerged in Embryophytes by incorporating a Type-I AT-hook motif at the N-terminus of the PPC domain, forming primitive Type-I AHL protein(s). The AHL genes were further duplicated and gradually evolved into two clades (Clade-B with newly emerged Type-II AHLs by incorporating one Type-II AT-hook and Clade-A with Type-I AHLs). Along the evolutionary division into the two clades, the PPC domains in the AHL gene family were also evolved into two types. Through the evolution of modern land plants, members of the Type-II AHLs lost the Type-I AT-hook motif and gradually evolved into the Type-III AHLs.