“AN EXPLOSIVE EXPANSION of homeoprotein-encoding genes has accompanied the evolution of multicellularity in animals and land plants, with homeoprotein-based combinatorial control exerted over core domains of the body plan: PBC/MEIS + HOX proteins specify the anterior–posterior axis of animals, and KNOX + BELL proteins specify the initiation of the moss sporophyte program and regulate the architecture of shoot apical meristems.”
http://cshperspectives.cshlp.org/content/6/3/a016154.full