A chimeric AtMYB23 repressor induces hairy roots, elongation of leaves and stems, and inhibition of the deposition of mucilage on seed coats in Arabidopsis.

We reported previously that a chimeric repressor, in which a transcription factor was fused to the EAR motif repression domain, acted as a dominant repressor and suppressed the expression of target genes, such that resultant phenotypes were similar to those associated with loss-of-function alleles. We report here that expression of the chimeric AtMYB23 repressor induced a variety of morphological changes, namely the ectopic formation of root hairs, a short primary root, elongation of leaves and of inflorescence stems, and absence of the accumulation of mucilage on seed coats, in addition to disruption of the development of trichomes. The short primary root and the elongation of leaves and stems appeared to be due to the reduced and enhanced lengthwise expansion, respectively, of epidermal cells. Expression of the GL2 gene, which is involved in the formation of root hairs and the accumulation of mucilage, was suppressed in both the roots and siliques of the transgenic plants. In contrast, the expression of genes related to cell elongation, such as DWF1, SAUR, AQP, AGP15, DET3 and XET-1, was enhanced in leaves of the transgenic plants. Results suggest that the AtMYB23 transcription factor has the molecular function of regulating the development of epidermal cells not only in leaves but also in stems, roots and seeds. We describe that this type of chimeric repressor can be exploited as a useful tool for the functional analysis of redundant transcription factors.