Premium
In vitro binding of the tomato bZIP transcriptional activator VSF‐1 to a regulatory element that controls xylem‐specific gene expression
Author(s) -
TorresSchumann Sonia,
Ringli Christoph,
Heierli Daniel,
Amrhein Nikolaus,
Keller Beat
Publication year - 1996
Publication title -
the plant journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 3.058
H-Index - 269
eISSN - 1365-313X
pISSN - 0960-7412
DOI - 10.1046/j.1365-313x.1996.09030283.x
Subject(s) - promoter , gene , biology , microbiology and biotechnology , binding site , gene expression , regulatory sequence , genetics
The bean grp1.8 gene is specifically expressed in vascular tissue. Monomers and multimers of a 28 bp regulatory element of the grp1.8 promoter ( vs‐1 ) specifically activated both the −82 CaMV 35S and the −76/ grp1.8 minimal promoters in vascular tissue of transgenic tobacco plants. vs‐1 partially overlaps with a negative regulatory element in the grp1.8 promoter that is necessary for restriction of gene expression to vascular tissue. Nuclear extracts from tobacco and tomato cells contain a factor that binds to vs‐1 in vitro . To study the molecular basis of xylem‐specific expression mediated by the vs‐1 promoter element, a gene was isolated from tomato encoding a protein that binds to vs‐1 in vitro . This protein, designated VSF‐1, contains a bZIP motif close to the C‐terminus. Mutated vs‐1 elements were no longer bound by VSF‐1 and also failed to activate the minimal −82 CaMV 35S promoter in vivo . Transient expression of VSF‐1 in protoplasts stimulated vs‐1 dependent activation of the −76/ grp1.8 minimal promoter. Binding studies and use of a polyclonal antiserum against VSF‐1 provided further evidence that vs‐1 is a potential in vivo target site, as VSF‐1 was a part of the observed complex formed between vs‐1 and nuclear protein extract. vs‐1 does not contain the 5′‐ACGT‐3′ core sequence that is part of known plant bZIP protein binding sites or another palindromic sequence. Based on the unusual binding specificity and a characteristic amino acid sequence in the bZIP domain we propose that VSF‐1 and the partially homologous PosF21, a bZIP protein from Arabidopsis , belong to a new family of plant bZIP proteins.