Specific interaction of the tomato bZIP transcription factor VSF-1 with a non-palindromic DNA sequence that controls vascular gene expression.
The grp1.8 gene of French bean (Phaseolus vulgaris) is specifically expressed in vascular tissue and encodes a glycine-rich structural protein (GRP1.8) of the cell wall. Earlier promoter analysis had shown that a 28 bp fragment of the grp1.8 promoter (vs-1) confers vascular expression to heterologous minimal promoters and is bound by the tomato bZIP transcription factor VSF-1. Here, we analysed the interaction of VSF-1 with fragments of the vs-1 element and studied the molecular basis of specific binding both in the DNA sequence of the promoter element as well as in the protein. The minimal binding site of VSF-1 is a 9 bp, non-palindromic sequence with two non-identical half-sites and a central nucleotide which separates them. The amino acid sequence of the VSF-1 DNA-binding basic domain has a Lys at position -10 instead of a conserved Arg found in the other bZIP factors isolated so far. This lysine was found to be required for specific recognition of the non-palindromic binding site: a mutant VSF-1 with a Lys-to-Arg substitution at position -10 bound with higher affinity to a palindromic sequence than the wild-type protein. The minimal binding site of VSF-1 was sufficient and necessary to confer vascular-specific expression to a heterologous promoter in vivo. The vsf-1 promoter also showed vascular-specific expression in transgenic tobacco. The close similarity of these expression patterns suggests that VSF-1 is specifically involved in vascular expression of the grp1.8 gene in plants.
Ringli
C
C
Department of Resistance and Quality Breeding, Swiss Federal Research Station for Agroecology and Agriculture, Zürich, Switzerland.
Keller
B
B
D050976:Basic-Leucine Zipper Transcription Factors; D001665:Binding Sites; D018744:DNA, Plant / Q000378:metabolism; D019281:Dimerization; D018506:Gene Expression Regulation, Plant; D017343:Genes, Plant; D017930:Genes, Reporter; D016350:Leucine Zippers; D018551:Solanum lycopersicum / Q000033:anatomy & histology / Q000235:genetics*; D008239:Lysine; D008969:Molecular Sequence Data; D010940:Plant Proteins; D018547:Plant Stems / Q000033:anatomy & histology / Q000235:genetics; D011401:Promoter Regions, Genetic; D011485:Protein Binding; D014018:Tissue Distribution; D014157:Transcription Factors / Q000235:genetics*
D050976:Basic-Leucine Zipper Transcription Factors; D018744:DNA, Plant; D010940:Plant Proteins; D014157:Transcription Factors; C113854:VSF-1 protein, Lycopersicon esculentum; D008239:Lysine