Untitled

Abstract

We are interested in the regulatory mechanisms responsible for the mesophyll-specific expression of C4 phosphoenolpyruvate carboxylase (PEPCase). A one-hybrid screen resulted in the cloning of four different members of a novel class of plant homeodomain proteins, which are most likely involved in the mesophyll-specific expression of the C4 PEPCase gene in C4 species of the genus Flaveria. Inspection of the homeodomains of the four proteins reveals that they share many common features with homeodomains described so far, but there are also significant differences. Interestingly, this class of homeodomain proteins occurs also in Arabidopsis thaliana and other C3 plants. One-hybrid experiments as well as in vitro DNA binding studies confirmed that these novel homeodomain proteins specifically interact with the proximal region of the C4 PEPCase gene. The N-terminal domains of the homeodomain proteins contain highly conserved sequence motifs. Two-hybrid experiments show that these motifs are sufficient to confer homo- or heterodimer formation between the proteins. Mutagenesis of conserved cysteine residues within the dimerization domain indicates that these residues are essential for dimer formation. Therefore, we designate this novel class of homeobox proteins ZF-HD, for zinc finger homeodomain protein. Our data suggest that the ZF-HD class of homeodomain proteins may be involved in the establishment of the characteristic expression pattern of the C4 PEPCase gene.

Pathogen-induced binding of the soybean zinc finger homeodomain proteins GmZF-HD1 and GmZF-HD2 to two repeats of ATTA homeodomain binding site in the calmodulin isoform 4 (GmCaM4) promoter

“…We found that each GmZF-HD protein has two highly conserved putative zinc finger domains in the N-terminus and a DNA binding homeodomain in the C-terminus, which is characteristic of homologs in the plant ZF-HD family, including AtHB24 and −26 of the C3 plant Arabidopsis thaliana and FtHB1 of the C4 plant Flaveria trinervia (Figure 4A). The ZF-HD class of homeodomain proteins may be involved in the photosynthesis-related mesophyll-specific gene expression of phosphoenolpyruvate carboxylase in C4 species of the genus Flaveria (32). More recently, it was proposed that ZF-HD transcriptional regulators play overlapping regulatory roles in Arabidopsis floral development (33).…”

“…To better understand the mechanism of this response, the localization of GmZF-HD1 and −2 before and after pathogen exposure must be determined. Members of the ZF-HD family have two highly conserved N-terminal zinc finger domains and a C-terminal homeodomain (32). Interestingly, Windhövel et al .…”

“…Interestingly, Windhövel et al . (32) demonstrated that the two conserved N-terminal motifs constitute a novel dimerization domain that is involved in homo- or heterodimer formation. Mutagenesis of the second zinc finger domain showed that highly conserved cysteine residues are essential for protein–protein interaction (32).…”

“…(32) demonstrated that the two conserved N-terminal motifs constitute a novel dimerization domain that is involved in homo- or heterodimer formation. Mutagenesis of the second zinc finger domain showed that highly conserved cysteine residues are essential for protein–protein interaction (32). In the case of GmZF-HD1 and −2, their binding to ATTA repeats in the GmCaM4 promoter may not require dimerization (either homo- or heterodimerization) since a mutant deleted for the N-terminal ZF (i.e.…”

Stress induced and nuclear localized HIPP26 from Arabidopsis thaliana interacts via its heavy metal associated domain with the drought stress related zinc finger transcription factor ATHB29

“…Yeast two-hybrid analyses revealed that the ZF-HD proteins tend to form homo-and heterodimers which might play an important role in the interaction with the DNA and therefore might be involved in transcriptional regulation (Tan and Irish 2006). It could be shown that the homeodomain inherits DNA binding and the zinc-finger domain with its zinc is important for the dimerization (Windhövel et al 2001).…”