Phylogenetic classification and molecular evolution of knotted1 homeobox genes

Homeobox genes encode a family of DNA-binding regulatory proteins which are crucial for development. The first plant homeobox gene identified was knot ten1 which plays a major role in leaf development. The knotted1 gene has a homeobox which encodes a homeodomain (HD) and HD proteins have been shown t o function as transcription factors. A phylogenetic classification of the K NOTTED1 HD is presented. Here, we report six kn1 HDs from the cereals oat, barley, wheat, rye and rice. The KN1 class-I and -II genes can be divided i nto two distinct clades. Further, we hypothesize that KN1 and BELL1/MEIS HD s, (the closest non-KN1 class HDs evolved from a common ancestor after dive rgence from the common precursor of all the homeobox genes. Our analysis cl early shows the presence of an ancestral KN1 HD from which all the known pl ant kn1 class of genes evolved.