Homeodomain leucine zipper class I genes in Arabidopsis. Expression patterns and phylogenetic relationships.

Members of the homeodomain leucine zipper (HDZip) family of transcription factors are present in a wide range of plants, from mosses to higher plants, but not in other eukaryotes. The HDZip genes act in developmental processes, including vascular tissue and trichome development, and several of them have been suggested to be involved in the mediation of external signals to regulate plant growth. The Arabidopsis (Arabidopsis thaliana) genome contains 47 HDZip genes, which, based on sequence criteria, have been grouped into four different classes: HDZip I to IV.

The homeobox genes ATHB12 and ATHB7 encode potential regulators of growth in response to water deficit in Arabidopsis.

The Arabidopsis thaliana homeodomain leucine-zipper gene ATHB7 , which is active specifically under water deficit conditions, is proposed to act as a negative regulator of growth (Soderman et al ., 1996, Plant J. 10: 375 381; Hjellstrom et al .