The Wheat Transcriptional Activator SPA: A Seed-Specific bZIP Protein That Recognizes the GCN4-Like Motif in the Bifactorial Endosperm Box of Prolamin Genes

Abstract

The conserved bifactorial endosperm box found in the promoter of wheat storage protein genes comprises two different cis elements that are thought to be involved in regulating endosperm-specific gene expression. Endosperm nuclear extracts contain binding activities. One is called ESBF-I, which binds to the endosperm motif (EM), and the other is called ESBF-II, which binds to the GCN4-like motif(GLM). Here, we present a functional analysis of the endosperm box of a low-molecular-weight glutenin gene found on the 1D1 chromosome of hexaploid wheat (LMWG-1D1) in transgenic tobacco plants. Our analysis demonstrates the necessity of the EM and GLM for endosperm-specific gene expression and suggests the presence in tobacco of functional counterparts of wheat ESBF-I and ESBF-II. Furthermore, we describe the isolation and characterization of cDNA clones encoding SPA, a seed-specific basic leucine zipper protein from wheat that can activate transcription from the GLMs of the -326-bp LMWG-1D1 promoter in both maize and tobacco leaf protoplasts. This activation is also partially dependent on the presence of functional EMs, suggesting interactions between SPA with ESBF-I-like activities.

Expression of an Arabidopsis Aspartate Kinase/Homoserine Dehydrogenase Gene Is Metabolically Regulated by Photosynthesis-Related Signals but Not by Nitrogenous Compounds1

“…This result is of special interest, since expression of the AK/ HSD gene was not affected by nitrogenous compounds, whereas previous studies showed that a similar element was responsible for a nitrogen-regulated expression of storage protein genes (Muller and Knudsen, 1993;Albani et al, 1997). A possible explanation for this result is that plants may possess a gene family of GCN4-related transcription factors, which are differentially expressed in various tissues and under various physiological conditions, and which regulate a wide range of genes by binding to common GCN4 elements in their promoters.…”

“…1B). This element is present in a number of plant gene promoters (Muller and Knudsen, 1993) and was previously shown to regulate the seed-specific and nitrogen-dependent expression of storage protein genes (Muller and Knudsen, 1993;Albani et al, 1997). It was thus interesting to test whether this truncated promoter could still respond to Suc.…”

A Pivotal Role of the Basic Leucine Zipper Transcription Factor bZIP53 in the Regulation ofArabidopsisSeed Maturation Gene Expression Based on Heterodimerization and Protein Complex Formation

“…An understanding of gene expression control in the seed was tackled from early studies in plant molecular biology, with maize (Zea mays) Opaque2 (O2) representing a hallmark as one of the first plant transcription factor (TF) genes cloned and characterized (Hartings et al, 1989;Schmidt et al, 1990). Similarly, orthologous genes from wheat (Triticum aestivum) (SPA) and barley (Hordeum vulgare) (BLZ2) play the same roles as O2 in their corresponding species (Albani et al, 1997;Oñ ate et al, 1999). In dicot species, key TFs have been characterized that control gene expression programs during seed maturation.…”

Genomic regions influencing gene expression of the HMW glutenins in wheat

“…The common effect on the retained cis elements was initiated by putative trans factors residing on chromosomes 2BS, 7BS, 4DS, 5DS and 6DS. Potential transcription factors include the SPA, a seed-specific basic leucine zipper protein, bZIP, Dof prolamin box binding factor and a MYB-protein, possibly interacting with the Dof protein (Albani et al 1997;Vicente-Carbajosa et al 1997;Diaz et al 2002). Trans factors on the homoeologous chromosome arms did not produce the same effects (though there are other, minor examples in Table 1-2BS:2DS, 3AL:3DL, 6AL:6DL, 6AS:6DS and 7AS:7BS-of possible shared homoeologous trans regulators).…”

“…Anderson et al (2002) characterized 5 0 and 3 0 DNA of HMW glutenins and identified potential matrix-attachment regions (MARs), transposable elements (MITEs), and retrotransposons (LTR and non-LTR) flanking respective glutenin genes. Proposed transcription factors recognize conserved elements of glutenin promoters: the storage protein activator (SPA), a seed-specific basic leucine zipper protein, bZIP (Albani et al 1997), DNA binding with one finger (Dof) prolamin box binding factor (VicenteCarbajosa et al 1997) and a MYB-protein, possibly interacting with the Dof protein (Diaz et al 2002). Wheat and other cereals share cis motifs and trans domains for the regulation of storage and possibly other proteins.…”