Arabidopsis ABI5 Subfamily Members Have Distinct DNA-Binding and Transcriptional Activities

Abstract

A small family of novel basic leucine zipper proteins that includes abscisic acid (ABA)-INSENSITIVE 5 (ABI5) binds to the promoter region of the lea class gene Dc3. The factors, referred to as AtDPBFs (Arabidopsis Dc3 promoter-binding factors), were isolated from an immature seed cDNA library. AtDPBFs bind to the embryo specification and ABA-responsive elements in the Dc3 promoter and are unique in that they can interact with cis-elements that do not contain the ACGT core sequence required for the binding of most other plant basic leucine zipper proteins. Analysis of full-length cDNAs showed that at least five different Dc3 promoter-binding factors are present in Arabidopsis seeds; one of these, AtDPBF-1, is identical to ABI5. As expected, AtDPBF-1/ABI5 mRNA is inducible by exogenous ABA in seedlings. Despite the near identity in their basic domains, AtDPBFs are distinct in their DNA-binding, dimerization, and transcriptional activity.LEA (late embryogenesis abundant) genes as a group are highly expressed during late stages of embryo development (Hughes and Galau, 1991;Thomas, 1993;Parcy et al., 1994). lea gene products are ubiquitous among higher plants, and they are probably involved in the protection of cells from dehydration (Dure et al., 1989; Dure, 1993; Ingram and Bartels, 1996;Xu et al., 1996). Expression of many lea genes is not only seed specific but is also inducible by abscisic acid (ABA) or environmental stresses such as drought and high salinity (Skriver and Mundy, 1990; Chandler and Robertson, 1994; Ingram and Bartels, 1996).Dc3 is a carrot (Daucus carota) lea class gene that is abundantly expressed during somatic embryogenesis (Wilde et al., 1988). The Dc3 promoter drives ␤-glucuronidase (GUS) reporter gene expression in developing seeds of transgenic tobacco (Nicotiana tabacum) and in nonembryonic tissues exposed to exogenous ABA and conditions of water deficit (Seffens et al., 1990;Vivekananda et al., 1992;Siddiqui et al., 1998). Analysis of the Dc3 promoter revealed minimal sequences necessary for embryo-specific expression residing within a 117-bp region including the transcription start site (Thomas, 1993; Chung, 1996;Thomas et al., 1997). However, this proximal promoter region (PPR) is not sufficient for ABAinduced expression; the distal promoter region (DPR), located between Ϫ314 and Ϫ287, is also required for ABA response in addition to the PPR (Chung, 1996;Thomas et al., 1997). The PPR contains five related cis regulatory elements required for expression in embryogenesis; these elements (E motifs) share the consensus sequence ACACNNG. Elements with NNNCGTGT consensus are repeated within the minimal DPR. These latter elements are similar to the E motifs. The function of these elements has been demonstrated in planta (Chung, 1996).Protein-binding studies showed that similar, seedspecific, or ABA-inducible protein factors bind to the PPR and the DPR. Competition DNA-binding assays indicated that similar factors can bind to both the PPR and the DPR. Genes encoding these Dc3 promoterbindin...

Integration of light and abscisic acid signaling during seed germination and early seedling development

“…4 C and M). ABI5 transcripts could be detected in floral tissues (24), which is coincident with the high accumulation of HY5 protein in floral tissues (25). Consistently, ABI5::GUS activity is barely detectable in hy5 floral tissues, in contrast to the strong GUS staining in the wild type (Fig.…”

Cytoplasmic Degradation of the Arabidopsis Transcription Factor ABSCISIC ACID INSENSITIVE 5 Is Mediated by the RING-type E3 Ligase KEEP ON GOING

“…ABI5 and ABI5-related bZIP transcription factors (AREBs (ABA responsive element-binding proteins), ABFs (ABRE binding Factors), and/or DPBFs (Dc3 promoter binding factors)), all possess similar domain architecture, consisting of a bZIP DNA-binding domain and four highly conserved regions, C1-C4 (25)(26)(27). The interaction between KEG and ABI5 occurs via the conserved C3 region of ABI5.…”

“…No interaction was observed with KEG , which lacks the ankyrin repeats. ABI5 contains a conserved bZIP DNA-binding domain and four highly conserved regions, C1-C4 (25,26) (Fig. 2C).…”

Gibberellin Biosynthesis and Response during Arabidopsis Seed Germination[W]

“…A basic domain/Leu zipper transcription factor, ABI5, binds to ABRE (Kim et al, 2002), and another transcription factor, ABI3, binds to a sequence called a Sph/RY element (Suzuki et al, 1997;Ezcurra et al, 2000), which often is found adjacent to ABREs. Because both abi3 and abi5 confer ABA insensitivity and they behave as recessive mutations, ABI3 and ABI5 are positive regulators of the ABA response (Finkelstein et al, 2002).…”