Sequence Analysis and Expression Patterns Divide the Maize Knotted1-like Homeobox Genes into Two Classes

The homeobox of the knotted1 (kn1) gene was used to isolate 12 related sequences in maize. The homeodomains encoded by the kn1-like genes are very similar, ranging from 55 to 89% amino acid identity. Differences outside the precisely conserved third helix allowed us to group the genes into two classes. The homeodomains of the seven class 1 genes share 73 to 89% identical residues with kn1. The four class 2 genes share 55 to 58% identical residues with kn1, although the conservation within the class is greater than 87%. Expression patterns were analyzed by RNA gel blot analysis. Class 1 genes were highly expressed in meristem-enriched tissues, such as the vegetative meristem and ear primordia. Expression was not detectable in leaves. The class 2 genes were expressed in all tissues, although one was abundantly expressed in roots. The genes were mapped using recombinant inbred populations. We determined that clusters of two to three linked genes are present on chromosomes 1 and 8; otherwise, the genes are distributed throughout the genome. Four pairs of genes, similar in both sequence and expression patterns, mapped within duplicated regions of the genome.