Characterization of Arabidopsis ZIM, a member of a novel plant-specific GATA factor gene family

The Arabidopsis gene ZIM encodes a putative transcription factor containing a novel GATA-type zinc-finger domain with a longer spacer between its two sets of conserved cysteine residues (C-X-2-C-X-20-C-X-2-C). In Arabidopsis, ZIM and homologous proteins, ZML1 and ZML2, were identified as GATA factors containing the C-X-2-C-X-20-C-X-2-C motif, a CCT domain, and an uncharacterized conserved domain. Proteins that possess this domain structure were found exclusively in plants, indicating that they belong to a novel family of plant-specific GATA-type transcription factors. When ZIM was overexpressed using a CaMV 35S promoter in Arabidopsis, hypocotyls and petioles were elongated. The elongation phenotype was observed under all wavelengths of light tested and even in the presence of biosynthetic inhibitors of either brassinosteroid or gibberellin. In ZIM-overexpressing plants, XTH33 which is predicted to function in cell wall modification was detected as an up-regulated gene by microarray analysis, and this could account for the elongation phenotype. Genes in ZIM-overexpressing plants were identified that were up-regulated in a tissue-specific manner, which suggests that transcriptional regulation by ZIM and its consequent effects are spatially controlled.