A Conserved Domain of the viviparous-1 Gene Product Enhances the DNA Binding Activity of the bZIP Protein EmBP-1 and Other Transcription Factors

Abstract

The maize VP1 protein is a seed-specific regulator of gene expression that effects the expression of a subset of abscisic acid (ABA)-regulated genes that are expressed during the maturation program of the seed. In addition, VP1 has pleiotropic effects on seed development that are not related to ABA. In transient expression assays, VP1 has been shown to transactivate gene expression through at least two distinct promoter elements: the G boxes from the ABA-inducible wheat Em gene and the SphI box from the maize C1 gene. We have investigated how VP1 can transactivate gene expression through diverse promoter elements by analyzing its association in vitro with EmBP-1, a factor that binds the Em promoter. We demonstrate that VP1 can greatly enhance the DNA binding activity of EmBP-1 in a gel retardation assay. This enhancing activity has also been observed on transcription factors as diverse as Opaque-2, Max, Sp1, and NF-B. Deletion of a small but highly conserved region (BR2) in VP1 eliminates the enhancement in vitro as well as the ability of VP1 to transactivate Em gene expression in a transient expression assay. A 40-amino acid fragment from VP1 sandwiched between the maltose-binding protein and LacZ can confer the enhancement function to this fusion protein in vitro. A weak and relatively nonspecific interaction between BR2 and DNA is demonstrated by UV cross-linking. The in vitro properties we observe for VP1 might explain the regulatory effects of VP1 on a diverse set of genes and why mutations in the vp1 locus have pleiotropic effects.

Functional Interactions of Lanthanum and Phospholipase D with the Abscisic Acid Signaling Effectors VP1 and ABI1-1 in Rice Protoplasts

“…2, B-D), as previously reported for the Em promoter (18,48,66). Furthermore, there was a significant (p Ͻ 0.07) interaction between lanthanum and VP1 in ABA-inducible gene expression that could be seen in the presence or absence of 100 M ABA (Fig.…”

“…To place the site of action of PLD in an ABA signaling cascade, we performed interaction studies between 1-butanol and two agonists of ABA-inducible gene expression, the transcription factor VP1 and the trivalent ion lanthanum (18,48,65,66). The results are shown in Table III (Table III).…”

“…The resulting 3.7-kilobase pair fragment (pCR559 minus the Em promoter) was then gel-purified and ligated with the 2-kilobase pair SphI/SmaI fragment of pAHC27, encoding the maize Ubi promoter (63). Plasmid pCR349.13S contains the 35 S promoter driving VP1 sense cDNA (18). Plasmid pG2 encodes the cauliflower mosaic virus 35 S promoter-maize C4 pyruvateorthophosphate dikinase (Ppdk35S) promoter chimera driving the coding region of the Arabidopsis thaliana abi1-1 dominant-negative G180D mutant allele (46).…”

The Transcription Factors HvABI5 and HvVP1 Are Required for the Abscisic Acid Induction of Gene Expression in Barley Aleurone Cells

“…Molecular analysis of the vp1 mutant has shown that the seeds do not accumulate ABA-regulated Lea genes such as rab17 (Pla et al, 1989) and the maize ortholog of the wheat Em gene (McCarty et al, 1991), suggesting its involvement in ABA-regulated gene expression. The expression of some ABA response genes, such as Em, Osem, and HVA1, has been reported to be activated by VP1 (Hattori et al, 1995;Hill et al, 1996;Shen et al, 1996). In this study, using an HvVP1-RNAi construct, we demonstrated that VP1 also is required for the activation of HVA1 and HVA22 promoters by ABA in aleurones (Figure 6).…”

Regulation of the ABA-responsive Em promoter by ABI3 in the moss Physcomitrella patens

“…7 The B1 domain is involved in physical interaction with the bZIP transcription factor ABI5 that binds to the ACGT core-containing ABA-responsive element (ABRE). [8][9][10] The B2 domain contains a putative nuclear localization signal (NLS), 11 is responsible for ABA-dependent activation through ABRE, [12][13][14][15] and also facilitates interaction with ABI5. 12 In addition, ABI3/VP1 transactivates gene promoters through the B3 DNA binding domain that recognizes the RY (or Sph) elements 7,16 found in the 5' regions of MAT genes, such as C1 in maize or 2S albumin genes in Arabidopsis and Brassica napus.…”