Isolation of homeodomain-leucine zipper genes from the moss Physcomitrellapatens and the evolution of homeodomain-leucine zipper genes in land plants

Homeobox genes encode transcription factors involved in many aspects of dev elopmental processes. The homeodomain-leucine zipper (HD-Zip) genes, which are characterized by the presence of both a homeodomain and a leucine zippe r motif. form a clade within the homeobox superfamily and were previously r eported only from vascular plants. Here we report the isolation of 10 HD-Zi p genes (named Pphb1-Pphb10) from the moss Physcomitrella patens. Based on a phylogenetic analysis of the 10 Pphb genes and previously reported vascul ar plant HD-Zip genes, all of the Pphb genes except Pphb3 belong to three o f the four HD-Zip subfamilies (HD-Zip I, II, and III), indicating that thes e subfamilies originated before the divergence of the vascular plant and mo ss lineages. Pphb3 is sister to the HD-Zip II subfamily and has some distin ctive characteristics, including the difference of the a, and d(1) sites of its leucine zipper motif, which are well conserved in each HD-Zip subfamil y. Comparison of the genetic divergence of representative HD-Zip I and II g enes showed that the evolutionary rate of HD-Zip I genes was faster than th at of HD-Zip II genes.