In vitro binding of the tomato bZIP transcriptional activator VSF‐1 to a regulatory element that controls xylem‐specific gene expression

Abstract

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.

A bZIP Protein, VIP1, Is a Regulator of Osmosensory Signaling in Arabidopsis

“…vascular-specific gene expression and thus vascular development (Torres-Schumann et al, 1996;Dai et al, 2003Dai et al, , 2004. The growth of VIP1-GFPox and vip1-1 was similar to the growth of wild-type plants (Fig.…”

RF2b, a rice bZIP transcription activator, interacts with RF2a and is involved in symptom development of rice tungro disease

“…RF2a and RF2b are members of a subgroup of plant bZIP proteins with DNA-binding sites common to several vascular specific promoters (15,19,28,35). The DNA-binding domains of RF2a, RF2b, and other bZIP proteins in this group are very highly conserved (Fig.…”

Promoter elements required for phloem‐specific gene expression from the RTBV promoter in rice

“…Another important element for phloem-specific expression of the RTBV promoter is the ASL Box, which acts synergistically with Box II to confer tissue-specific expression (Figure 4, middle panel) Top panel: Box II was compared with AC-I and AC-II of the PAL2 promoter (Hatton et al, 1995), the footprint 4 of the 4CL promoter (Hauffe et al, 1993), vs-1 of the grpl.8 promoter (Torres-Schumann et al, 1996) as well as proximal promoter sequences of SH1 (Werr et al, 1985;Yang and Russel, 1990), AHA3 gene (Dewitt et al, 1991). The characteristic CCA/TGG repeat are indicated by arrows and the conserved CCCC sequences are boxed.…”