Expression patterns of novel genes encoding homeodomain leucine-zipper proteins in Arabidopsis thaliana.

A recently discovered class of genes in Arabidopsis thaliana encode putative transcription factors which contain a homeodomain closely linked to a leucine zipper motif. We have previously reported on the cloning and cDNA sequence of one gene of this class, Athb-3. In this article we show this gene to be expressed predominantly in the cortex of the root and the stem. Using the Athb-3 clone as a probe we have isolated cDNA clones corresponding to three novel homeodomain-leucine zipper proteins. These clones, Athb-5, Athb-6 and Athb-7, hybridized to transcripts that were relatively abundant in the leaf, but also present in other vegetative organs, as well as in the flower. Only weak hybridization was observed to seed pod samples. These observations indicate that these Athb genes have major functions in the mature plant, and therefore, in contrast to homeobox genes in other eukaryotes and to the kn-1 gene in maize, are unlikely to function in the primary control of developmental processes during embryogenesis or organogenesis. The deduced amino acid sequences of Athb-5, Athb-6 and Athb-7 are highly similar to the previously isolated Athb-1, Athb-2 and Athb-3 in the homeodomain and leucine-zipper parts of the proteins, whereas the similarities to homeodomain proteins from other eukaryotes are limited. The Athb proteins thus constitute a new and well defined class of homeodomain proteins, apparently unique to plants.