title: HD-Zip proteins of families I and II from rice: interactions and functional properties.
abstract: Proteins of the closely related homeodomain-leucine zipper (HD-Zip) families I and II in plants are putative transcription factors that interact with similar pseudopalindromic DNA recognition sites. We have previously described the Oshox1 gene from rice, which encodes an HD-Zip II protein. To identify further rice HD-Zip proteins, one-hybrid screens were performed in yeast strains containing a HIS3 reporter gene with upstream HD-Zip recognition sites. This resulted in the isolation of six new cDNAs encoding HD-Zip proteins belonging to family I (Oshox4, -5, -6) or family II (Oshox2, -3, -7). In transient assays, using rice suspension-cultured cells transformed by particle bombardment, we showed previously that Oshox1 can transcriptionally repress the activity of reporter gene constructs with upstream HD-Zip binding sites. Here, we confirm the repression properties of Oshox1 by showing that the repression function can be conferred on a heterologous DNA-binding domain. This portable functional domain (residues 1-155) is located proximal to the HD-Zip domain. In yeast, the same region of the Oshox1 protein was found to confer transcriptional activation instead of repression, pointing to the possibility that cell type-specific factors may determine the functional properties of the Oshox1 protein in rice. Like Oshox1, another HD-Zip family II protein (Oshox3) was also found to function as a transcriptional repressor in rice cells. In contrast, two HD-Zip I family proteins (Oshox4 and -5) appeared to act as activators in both rice and yeast cells. Results of two-hybrid assays and electrophoretic mobility shift assays strongly suggest that all HD-Zip proteins of families I and II can form homodimers and also heterodimers with all HD-Zip proteins of the same family. Heterodimerization across the HD-Zip families I and II apparently does not to occur.
authors.affiliation: Institute of Molecular Plant Sciences, Leiden University, Clusius Laboratory, The Netherlands. meijer@rulbim.leidenuniv.nl
authors.forename: A H
authors.initials: AH
authors.lastname: Meijer
authors.forename: R J
authors.initials: RJ
authors.lastname: de Kam
authors.forename: I
authors.initials: I
authors.lastname: d'Erfurth
authors.forename: W
authors.initials: W
authors.lastname: Shen
authors.forename: J H
authors.initials: JH
authors.lastname: Hoge
mesh_terms: D020816:Amino Acid Motifs; D000595:Amino Acid Sequence; D003001:Cloning, Molecular; D018076:DNA, Complementary / Q000235:genetics / Q000302:isolation & purification; D018744:DNA, Plant / Q000235:genetics / Q000302:isolation & purification; D019281:Dimerization; D017930:Genes, Reporter; D018398:Homeodomain Proteins / Q000737:chemistry / Q000235:genetics* / Q000378:metabolism; D007763:Lac Operon; D016350:Leucine Zippers / Q000235:genetics; D008969:Molecular Sequence Data; D012275:Oryza / Q000235:genetics*; D010940:Plant Proteins / Q000737:chemistry / Q000235:genetics* / Q000378:metabolism; D020836:Protein Structure, Quaternary; D012441:Saccharomyces cerevisiae / Q000235:genetics; D017386:Sequence Homology, Amino Acid; D014157:Transcription Factors / Q000737:chemistry / Q000235:genetics* / Q000378:metabolism; D015533:Transcriptional Activation; D020798:Two-Hybrid System Techniques
chemical_list: D018076:DNA, Complementary; D018744:DNA, Plant; C091850:HD-Zip protein, Helianthus annuus; D018398:Homeodomain Proteins; D010940:Plant Proteins; D014157:Transcription Factors