Constitutive expression of the water deficit-inducible homeobox gene ATHB7 in transgenic Arabidopsis causes a suppression of stem elongation growth

The Arabidopsis gene ATHB7 encodes a transcription factor of the homeodomain-leucine zipper class. The activity of the gene is dependent on the water conditions of the plant; expression being strongly induced in plants subjected to water deficit or to treatment with abscisic acid (ABA). In this report we demonstrate that ATHB7, when constitutively expressed at levels typical for plants exposed to water-deficit conditions, caused a reduction in elongation growth in the leaf and in the inflorescence stem. The reduction in stem growth mimics the effect on growth caused by water-deficit conditions, but is independent of water conditions in plants that express ATHB7 constitutively. These results indicate that ATHB7 in the wild-type plant may be a mediator of the plant growth response to limiting water conditions in the leaf and in the inflorescence stem. In support of this notion we also show that the ATHB7 promoter in wild-type plants exposed to water-deficit conditions is highly active in the elongating parts of the inflorescence stem as well as leaves.