Analyses of alpha/beta-type gliadin genes from diploid and hexaploid wheats

Interaction mechanism between cereal phenolic acids and gluten protein: protein structural changes and binding mode

BACKGROUND

Phenolic acids are antioxidant nutrients in cereals and affect the quality of wheat products and the properties of gluten protein. Gallic acid (GA), caffeic acid (CA), syringic acid (SA), and p-coumaric acid (p-CA) were selected to study the interaction mechanism between cereal phenolic acids and gluten protein.

RESULTS

The results showed that adding GA significantly (P < 0.05) decreased the content of free sulfhydryl in gluten proteins by 70-87.26% compared with the control group. The aggregates' behavior of gluten protein induced by adding the phenolic acids would produce oversized particles (>5000 nm). Adding the selected phenolic acids changed the hydrogen-bond linkage of protein secondary structure. Zeta potential values of gluten protein increased significantly (P < 0.05) by 14.41%, 26.49%, 30.77%, and 57.93% for CA, p-CA, GA, and SA respectively added at 0.03 g kg^-1 . Moreover, the gluten protein surface hydrophobicity increased when the phenolic acids were added at 0.03 g kg^-1 , displaying the effect of the phenolic acid on the hydrophobic interaction of protein. Molecular docking results showed that the selected phenolic acids could interact with glutenin and gliadin using hydrogen-bond formation, and SA had the strongest binding with glutenin and gliadin.

CONCLUSION

The results demonstrated that the selected phenolic acids could interact with gluten protein via covalent cross-linking as well as by hydrogen bonding, thereby changing the structure of the gluten protein. This exploration is expected to provide theoretical support for the development and utilization of whole-grain foods. © 2022 Society of Chemical Industry.

Genome-, Transcriptome- and Proteome-Wide Analyses of the Gliadin Gene Families in Triticum urartu

Gliadins are the major components of storage proteins in wheat grains, and they play an essential role in the dough extensibility and nutritional quality of flour. Because of the large number of the gliadin family members, the high level of sequence identity, and the lack of abundant genomic data for Triticum species, identifying the full complement of gliadin family genes in hexaploid wheat remains challenging. Triticum urartu is a wild diploid wheat species and considered the A-genome donor of polyploid wheat species. The accession PI428198 (G1812) was chosen to determine the complete composition of the gliadin gene families in the wheat A-genome using the available draft genome. Using a PCR-based cloning strategy for genomic DNA and mRNA as well as a bioinformatics analysis of genomic sequence data, 28 gliadin genes were characterized. Of these genes, 23 were α-gliadin genes, three were γ-gliadin genes and two were ω-gliadin genes. An RNA sequencing (RNA-Seq) survey of the dynamic expression patterns of gliadin genes revealed that their synthesis in immature grains began prior to 10 days post-anthesis (DPA), peaked at 15 DPA and gradually decreased at 20 DPA. The accumulation of proteins encoded by 16 of the expressed gliadin genes was further verified and quantified using proteomic methods. The phylogenetic analysis demonstrated that the homologs of these α-gliadin genes were present in tetraploid and hexaploid wheat, which was consistent with T. urartu being the A-genome progenitor species. This study presents a systematic investigation of the gliadin gene families in T. urartu that spans the genome, transcriptome and proteome, and it provides new information to better understand the molecular structure, expression profiles and evolution of the gliadin genes in T. urartu and common wheat.

The molecular diversity of α-gliadin genes in the tribe Triticeae

Many of the unique properties of wheat flour are derived from seed storage proteins such as the α-gliadins. In this study these α-gliadin genes from diploid Triticeae species were systemically characterized, and divided into 3 classes according to the distinct organization of their protein domains. Our analyses indicated that these α-gliadins varied in the number of cysteine residues they contained. Most of the α-gliadin genes were grouped according to their genomic origins within the phylogenetic tree. As expected, sequence alignments suggested that the repetitive domain and the two polyglutamine regions were responsible for length variations of α-gliadins as were the insertion/deletion of structural domains within the three different classes (I, II, and III) of α-gliadins. A screening of celiac disease toxic epitopes indicated that the α-gliadins of the class II, derived from the Ns genome, contain no epitope, and that some other genomes contain much fewer epitopes than the A, S(B) and D genomes of wheat. Our results suggest that the observed genetic differences in α-gliadins of Triticeae might indicate their use as a fertile ground for the breeding of less CD-toxic wheat varieties.

Cloning, expression, and evolutionary analysis of α-gliadin genes from Triticum and Aegilops genomes

Fifteen novel α-gliadin genes were cloned and sequenced from Triticum and related Aegilops genomes by allele-specific polymerase chain reaction (AS-PCR). Sequence comparison displayed high diversities in the α-gliadin gene family. Four toxic epitopes and glutamine residues in the two polyglutamine domains facilitated these α-gliadins to be assigned to specific chromosomes. Five representative α-gliadin genes were successfully expressed in Escherichia coli, and their amount reached a maximum after 4 h induced by isopropyl-β-D-thiogalactoside (IPTG), indicating a high level of expression under the control of T7 promoter. The transcriptional expression of α-gliadin genes during grain development detected by quantitative real-time polymerase chain reaction (qRT-PCR) showed a similar up-down regulation pattern in different genotypes. A neighbor-joining tree constructed with both full-open reading frame (ORF) α-gliadin genes and pseudogenes further revealed the origin and phylogenetic relationships among Triticum and related Aegilops genomes. The evolutionary analysis demonstrated that α-gliadin genes evolved mainly by synonymous substitutions under strong purifying selection during the evolutionary process.

Variations and classification of toxic epitopes related to celiac disease among α-gliadin genes from four Aegilops genomes

The α-gliadins are associated with human celiac disease. A total of 23 noninterrupted full open reading frame α-gliadin genes and 19 pseudogenes were cloned and sequenced from C, M, N, and U genomes of four diploid Aegilops species. Sequence comparison of α-gliadin genes from Aegilops and Triticum species demonstrated an existence of extensive allelic variations in Gli-2 loci of the four Aegilops genomes. Specific structural features were found including the compositions and variations of two polyglutamine domains (QI and QII) and four T cell stimulatory toxic epitopes. The mean numbers of glutamine residues in the QI domain in C and N genomes and the QII domain in C, N, and U genomes were much higher than those in Triticum genomes, and the QI domain in C and N genomes and the QII domain in C, M, N, and U genomes displayed greater length variations. Interestingly, the types and numbers of four T cell stimulatory toxic epitopes in α-gliadins from the four Aegilops genomes were significantly less than those from Triticum A, B, D, and their progenitor genomes. Relationships between the structural variations of the two polyglutamine domains and the distributions of four T cell stimulatory toxic epitopes were found, resulting in the α-gliadin genes from the Aegilops and Triticum genomes to be classified into three groups.

Cereal seed storage protein synthesis: fundamental processes for recombinant protein production in cereal grains

Cereal seeds provide an ideal production platform for high-value products such as pharmaceuticals and industrial materials because seeds have ample and stable space for the deposition of recombinant products without loss of activity at room. Seed storage proteins (SSPs) are predominantly synthesized and stably accumulated in maturing endosperm tissue. Therefore, understanding the molecular mechanisms regulating SSP expression and accumulation is expected to provide valuable information for producing higher amounts of recombinant products. SSP levels are regulated by several steps at the transcriptional (promoters, transcription factors), translational and post-translational levels (modification, processing trafficking, and deposition). Our objective is to develop a seed production platform capable of producing very high yields of recombinant product. Towards this goal, we review here the individual regulatory steps controlling SSP synthesis and accumulation.

Embryo and anther regulation of the mabinlin II sweet protein gene in Capparis masaikai Lévl

Mabinlin II is one of the major sweet proteins stored in the seeds of Capparis masaikai Lévl. Its promoter region (779 bp) located 5' upstream of the mabinlin II gene has been isolated and named as MBL-779 (GenBank accession number, EU014073). This promoter contains two typical TATA box regions and a series of motifs related to seed-specific promoters, such as ACGT motifs, RY motif, napin motif, and G box. The MBL-779 promoter drove GUS gene to transiently express in the embryos of bean, maize, and rice seeds or to constantly express in the embryos and anthers of the transgenic Arabidopsis. The MBL-779 promoter regulated gene expression from approximately the 12th day and peaked on approximately the 16th day after flowering in Arabidopsis. The -300-bp promoter region is a minimal sequence required to functionally regulate gene expression. The CAATs at -325 to -322 bp and -419 to -416 bp and the region at -485 to -770 bp play a role in the quantitative regulation of gene expression. The RY motif, CATGAC, at -117 to -112 bp and the ACGT within the G box (CACGTG) at -126 to -123 bp positively regulate gene expression.

Detailed analysis of the expression of an alpha-gliadin promoter and the deposition of alpha-gliadin protein during wheat grain development

BACKGROUND AND AIMS

Alpha-gliadin proteins are important for the industrial quality of bread wheat flour, but they also contain many epitopes that can trigger celiac (coeliac) disease (CD). The B-genome-encoded alpha-gliadin genes, however, contain very few epitopes. Controlling alpha-gliadin gene expression in wheat requires knowledge on the processes of expression and deposition of alpha-gliadin protein during wheat grain development.

METHODS

A 592-bp fragment of the promotor of a B-genome-encoded alpha-gliadin gene driving the expression of a GUS reporter gene was transformed into wheat. A large number of transgenic lines were used for data collection. GUS staining was used to determine GUS expression during wheat kernel development, and immunogold labelling and tissue printing followed by staining with an alpha-gliadin-specific antibody was used to detect alpha-gliadin protein deposited in developing wheat kernels. The promoter sequence was screened for regulatory motifs and compared to other available alpha-gliadin promoter sequences.

KEY RESULTS

GUS expression was detected primarily in the cells of the starchy endosperm, notably in the subaleurone layer but also in the aleurone layer. The alpha-gliadin promoter was active from 11 days after anthesis (DAA) until maturity, with an expression similar to that of a 326-bp low molecular weight (LMW) subunit gene promoter reported previously. An alpha-gliadin-specific antibody detected alpha-gliadin protein in protein bodies in the starchy endosperm and in the subaleurone layer but, in contrast to the promoter activity, no alpha-gliadin was detected in the aleurone cell layer. Sequence comparison showed differences in regulatory elements between the promoters of alpha-gliadin genes originating from different genomes (A and B) of bread wheat both in the region used here and upstream.

CONCLUSIONS

The results suggest that additional regulator elements upstream of the promoter region used may specifically repress expression in the aleurone cell layer. Observed differences in expression regulator motifs between the alpha-gliadin genes on the different genomes (A and B) of bread wheat leads to a better understanding how alpha-gliadin expression can be controlled.

Characterization of a new rice glutelin gene GluD-1 expressed in the starchy endosperm

A new glutelin gene, designated GluD-1, has been discovered by comparing the seed storage proteins from 48 japonica and indica rice cultivars on SDS-PAGE gels. Evidence that GluD-1 is a member of the glutelin family was provided by Western blots using anti-glutelin antiserum and by mapping the gene to the chromosomal glutelin gene cluster. The limited GluD-1 size polymorphism among the rice varieties is due to amino acid substitutions rather than to post-transcriptional modification. GluD-1 is maximally expressed in the starchy endosperm starting at 5 d after flowering (DAF) and increasing through 30 DAF, a major difference from the other glutelins which are primarily expressed in the subaleurone from 10-16 DAF. Only about 0.2 kb of the GluD-1 promoter was sufficient to confer inner starchy endosperm-specific expression. The 0.2 kb truncated GluD-1 promoter contains a bifactorial endosperm box consisting of a truncated GCN4 motif (TGA(G/C)TCA) and AAAG Prolamin box (P box), and ACGT and AACA motifs as cis-regulatory elements. Gel retardation assays and trans-activation experiments indicated that the truncated GCN4 and P box are specifically recognized by RISBZ1 b-ZIP and RPBF Dof activators in vitro, respectively, and are synergistically transactivated, indicating that combinatorial interactions of these motifs are involved in essential endosperm-specific regulation. Furthermore, deviation from the cognate GCN4 motif alters tissue-specific expression in the inner starchy endosperm to include other endosperm tissues.

A novel cis-acting element, ESP, contributes to high-level endosperm-specific expression in an oat globulin promoter

To examine the genetic controls of endosperm (ES) specificity, several cereal seed storage protein (SSP) promoters were isolated and studied using a transient expression analysis system. An oat globulin promoter (AsGlo1) capable of driving strong ES-specific expression in barley and wheat was identified. Progressive 5' deletions and cis element mutations demonstrated that the mechanism of specificity in the AsGlo1 promoter was distinct from that observed in glutelin and prolamin promoters. A novel interrupted palindromic sequence, ACATGTCATCATGT, was required for ES specificity and substantially contributed to expression strength of the AsGlo1 promoter. This sequence was termed the endosperm specificity palindrome (ESP) element. The GCN4 element, which has previously been shown to be required for ES specificity in cereal SSP promoters, had a quantitative role but was not required for tissue specificity. The 960-bp AsGlo1 promoter and a 251-bp deletion containing the ESP element also drove ES-specific expression in stably transformed barley. Reporter gene protein accumulated at very high levels (10% of total soluble protein) in ES tissues of plants transformed with an AsGlo1:GFP construct. Expression strength and tissue specificity were maintained over five transgenic generations. These attributes make the AsGlo1 promoter an ideal promoter for biotechnology applications. In conjunction with previous findings, our data demonstrate that there is more than one genetically distinct mechanism by which ES specificity can be achieved in cereal SSP promoters, and also suggest that there is redundancy between transcriptional and post-transcriptional tissue specificity mechanisms in cereal globulin genes.

Genomic organization of the complex alpha-gliadin gene loci in wheat

To better understand the molecular evolution of the large alpha-gliadin gene family, a half-million bacterial artificial chromosome (BAC) library clones from tetraploid durum wheat, Triticum turgidum ssp. durum (2n = 4x = 28, genome AB), were screened for large genomic segments carrying the alpha-gliadin genes of the Gli-2 loci on the group 6 homoeologous chromosomes. The resulting 220 positive BAC clones--each containing between one and four copies of alpha-gliadin sequences--were fingerprinted for contig assembly to produce contiguous chromosomal regions covering the Gli-2 loci. While contigs consisting of as many as 21 BAC clones and containing up to 17 alpha-gliadin genes were formed, many BAC clones remained as singletons. The accuracy of the order of BAC clones in the contigs was verified by Southern hybridization analysis of the BAC fingerprints using an alpha-gliadin probe. These results indicate that alpha-gliadin genes are not evenly dispersed in the Gli-2 locus regions. Hybridization of these BACs with probes for long terminal repeat retrotransposons was used to determine the abundance and distribution of repetitive DNA in this region. Sequencing of BAC ends indicated that 70% of the sequences were significantly similar to different classes of retrotransposons, suggesting that these elements are abundant in this region. Several mechanisms underlying the dynamic evolution of the Gli-2 loci are discussed.

Molecular cloning, sequencing, and chromosome mapping of a 1A-encoded omega-type prolamin sequence from wheat

Gliadins are the most abundant component of the seed storage proteins in cereals and, in combination with glutenins, are important for the bread-making quality of wheat. They are divided into four subfamilies, the alpha-, beta-, gamma-, and omega-gliadins, depending on their electrophoresis pattern, chromosomal location, and DNA and protein structures. Using a PCR-based strategy we isolated and sequenced an omega-gliadin sequence. We also determined the chromosomal subarm location of this sequence using wheat aneuploids and deletion lines. The gene is 1858 bp long and contains a coding sequence 1248 bp in length. Like all other gliadin gene families characterized in cereals, the omega-gliadin gene described here had characteristic features including two repeated sequences 300 bp upstream of the start codon. At the DNA level, the gene had a high degree of similarity to the omega-secalin and C-hordein genes of rye and barley, but exhibited much less homology to the alpha- and beta-gliadin gene families. In terms of the deduced amino acid sequence, this gene has about 80 and 70% similarity to the omega-secalin and C-hordein genes, respectively, and possesses all the features reported for other gliadin gene families. The omega-gliadin gene has about 30 repeats of the core consensus sequences PQQPX and XQQPQQX, twice as many as other gliadin gene families. Southern blotting and PCR analysis with aneuploid and deletion lines for the short arm of chromosome 1A showed that the omega-gliadin was located on the distal 25% of the short arm of chromosome 1A. By comparison of PCR and A-PAGE profiles for deletion stocks, its genomic location must be at a different locus from gli-Ala in 'Chinese Spring'.

Intimate association of microsatellite repeats with retrotransposons and other dispersed repetitive elements in barley

Simple sequence repeat (SSR)-based genetic markers are being actively developed for the majority of crop plant species. In barley, characterization of 290 dinucleotide repeat-containing clones from SSR-enriched libraries has revealed that a high percentage are associated with cereal retrotransposon-like and other dispersed repetitive elements. Associations found were with BARE-1, WIS2-1A, PREM1 and the dispersed repetitive element R173. Additional similarities between different SSR clones, which have no matches in DNA sequence databases, indicate that this phenomenon is probably widespread in the barley genome. Sequence homologies to the non-coding regions of several cereal genes were also explained by homology to mobile genetic elements. The SSRs found can therefore be classified into two types: (1) those with unique sequences on either flank, and (2) those which are intimately associated with retro-transposons and other dispersed repetitive elements. As the cereal genome is thought to consist largely of this type of DNA, some random association would be expected. However, the conserved positions of the SSRs, relative to repetitive elements, indicate that they have arisen non-randomly. Furthermore, this class of SSRs can be classified into three subtypes: (1) those which are positioned 3' of a transposable element with unique sequence on the other flank, (2) those positioned 5' of a transposable element, and (3) those which have arisen from an internal sequence and so have transposable element sequence on both flanks. The first appear to be analogous to the class of SSRs in mammalian systems which are associated with Alu elements and SINEs (short interspersed elements) and which have been postulated to arise following integration of an extended and polyadenylated retro-transcript into the host genome, followed by mutation of the poly(A) tract and expansion into an SSR. For the second, we postulate that a proto-SSR (A-rich sequence) has acted as a 'landing pad' for transposable element insertion (rather than being the result of insertion), while the third includes those which have evolved as a component of an active transposable element which has spread throughout the genome during bursts of transposition activity. The implications of these associations for genome and SSR evolution in barley are discussed.

The promoter of the gene Itr1 from barley confers a different tissue specificity in transgenic tobacco

Tissue-specific expression of the gene coding for trypsin inhibitor BTI-CMe in barley (Itr1) occurs during the first half of endosperm development. In transgenic tobacco, the Itr1 promoter drives expression of the beta-glucuronidase reporter gene not only in developing endosperm but also in embryo, cotyledons and the meristematic intercotyledonary zone of germinating seedlings. A promoter fragment extending 343 bp upstream of the translation initiation ATG codon was sufficient for full transgene expression, whereas, the proximal 83 bp segment of the promoter was inactive. Possible reasons for the differences in expression patterns are discussed.

Characterization of distinct alpha- and gamma-type gliadins and low molecular weight components from wheat endosperm as coeliac immunoreactive proteins

Distinct alpha- and gamma-type gliadins, as well as a few low molecular weight components have been identified as coeliac immunoreactive proteins from a chloroform/methanol extract from wheat endosperm. Characterization of these components involved the combination of reverse-phase high-performance liquid chromatography, immunoblotting following SDS-PAGE using a coeliac serum and microsequencing analysis. This has allowed the identification of a group of gliadins with different molecular weights, according to their N-terminal amino-acid sequence: five alpha-type gliadins of 31, 35, 38 and two of 45 kDa, one gamma 2-type gliadin of 40 kDa, two gamma 3-type gliadins of 31, and 50 kDa, and two gamma-type gliadins with an atypical gliadin N-terminal of 31, and 40 kDa, as well as a few unidentified low molecular weight components and three N-terminal blocked proteins, all exhibiting similar antigenicity.

Analysis of nuclear proteins interacting with a wheat alpha/beta-gliadin seed storage protein gene

The promoter region (-524 to -46) of the wheat alpha/beta-gliadin seed storage protein gene was analyzed for interactions with nuclear proteins from developing wheat seeds. Six complexes were detected within the first 165 bp upstream of the transcriptional start site. One of the proteins was a non-sequence specific AT-binding protein. The remaining five proteins bound in a sequence specific manner. One (CABP) mapped to a conserved CA-rich element at -134 to -112 while another (PalBP) mapped to an adjacent, palindromic sequence at -112 to -106. Three proteins (CTBPs 1-3) formed complexes at two, independent homologous sites. The activities of four of the binding proteins, CTBPs 1-3 and CABP, exhibited similar patterns of expression during seed development: they first appeared at early to mid stages, reached a maximum at mid stage and subsequently decreased, paralleling the pattern of gliadin mRNA accumulation. The non-specific AT-binding protein was detected at relatively high levels only at mid development. PalBP activity, on the other hand, first appeared at mid stage and was present at a constant level throughout later stages of development. The results suggest that the binding proteins may regulate gliadin expression in an antagonistic manner.

Gene structure and expression of rice seed allergenic proteins belonging to the alpha-amylase/trypsin inhibitor family

Genomic and two novel cDNA clones for rice seed allergenic protein (RA) belonging to the alpha-amylase/trypsin inhibitor family were isolated and their nucleotide sequences determined. Ten cysteine residues deduced from nucleotide sequences were completely conserved among three cDNA clones including a clone, RA17, reported previously. One genomic clone, lambda 4, contained two RA genes, RAG1 and RAG2. Although RAG1 was cloned at the 5' portion only, two RA genes were arranged divergently. Nucleotide sequencing and DNA blotting analyses showed that RA are encoded by a multigene family consisting of at least four members. The transcriptional initiation site of RAG1 was localized at A, 26 bp upstream of the putative translational initiation codon, ATG, by the primer extension assay. The putative TATA box and CAAT box existed about 45 bp and 147 bp upstream of the transcription initiation site, respectively. A conserved sequence (ATGCAAAA) which was similar to the sequence (TGCAAAA) identified in rice glutelin promoters was observed in the 5' region of the two genes. In addition, RNA blotting analyses provided that RA genes specifically expressed in ripening seed and their transcripts accumulated maximally between 15 and 20 days after flowering.

Purification and characterisation of antigenic gliadins in coeliac disease

Two gliadins, known to be especially antigenic in coeliac disease, were purified to homogeneity by a series of ion-exchange chromatography steps. Their N-terminal amino acid sequences showed minor differences but clearly classified them as gamma-type gliadins. The purified gliadins were further characterised with respect to amino acid composition, molecular mass and E1(1%)cm at 276 nm. Based on these properties it is suggested that one of them is identical to a gamma-type gliadin, earlier characterised by its nucleotide sequence, whereas the other has not previously been described. The purification procedure may form the basis for the development of a more differentiated analysis of circulating antibodies for diagnosis and makes clinical testing of the toxicity of defined gliadin peptides feasible.

Coeliac active peptides from gliadin: large-scale preparation and characterization

Larger amounts of coeliac active peptides are required for pathogenetic investigations. Therefore, a simplified preparative procedure by means of gel-permeation chromatography and reversed-phase HPLC was developed for the isolation of the peptides B3141-B3146, which are present in peptic tryptic digests of gliadin [this journal (1983) 176:85-94]. The peptides are derived from the N-terminal part of alpha-gliadins and are closely related. The amino acid sequence of B3143 is VPVPQLQPQNPSQQQPQEQVPLVQQQQFPGQQQQFPPQQPYPQPQPFPSQQPYL. B3144 has proline instead of glutamine in position 34. The previously described peptide B3142 [this journal (1984) 179:371-376] corresponds to B3144 except for the missing C-terminal leucine.

Chromosomal control of wheat gliadin protein epitopes: analysis with specific monoclonal antibodies

The genetic relationships between small clusters of monomeric alcohol-soluble wheat (Triticum aestivum L.) grain storage proteins (gliadins) were studied using a panel of monoclonal antibodies and immunoblotting, ELISA, and RIA methods. Use of Chinese Spring nullisomic-tetrasomic lines showed that several narrow-specificity antibodies bound specifically to gliadins encoded by genes located on a single chromosome. In at least one case, antibodies bound to genetic "blocks" of gliadins, indicating that these block members have structural homology. However, often not all gliadins of a block were recognized by an antibody. For broad-specificity antibodies and some narrow-specificity antibodies, structural genes on several chromosomes were important. Studies with several primitive wheat species indicated that, while antibodies usually bound gliadins from the same genome in bread and primitive wheats, antibodies sometimes bound proteins of quite differing mobilities in the two wheat types. Use of antibodies to identify gliadin blocks is simpler than block analysis based on performing crosses, and should be of value in monitoring genotype/end-use quality relationships.

[Analysis of food and feed by partial sequences of characteristic protein components (carrier peptides). 1. Isolation and structural determination of wheat-specific peptides from chymotryptic hydrolysates of gliadin]

Gliadins from wheat flour were extracted with 70% aqueous ethanol and hydrolyzed with alpha-chymotrypsin. Eight peptides, which seemed adequate as specific indicators for wheat ('Leitpeptide'), were isolated from the partial hydrolysate by RP-HPLC and analyzed for their amino acid sequences. Six of them were attributed to gliadin sequences already described in the literature, whereas two peptides represented novel sequence variations. Parallel investigations on the corresponding partial hydrolysates of prolamins from rye, barley, oats and maize showed that the isolated peptides were specific for wheat. A search in the protein data bank MIPS X (as of January 23 rd, 1990) did not produce any identical sequence. The 'Leitpeptide' allows the sensitive and specific recognition of wheat in complex and heated systems by RP-HPLC. They could be used also as the basis for immunochemical tests which would be convenient in routine analysis.

Structural and functional analysis of promoter from gliadin, an endosperm-specific storage protein gene of Triticum aestivum L

To identify cis-regulatory elements of the gliadin gene, a study of the gliadin gene promoter was conducted by transient expression analysis of plasmid DNAs which were introduced into plant protoplasts by electroporation. The promoter region (-592 bp to +18 bp from the translational start) of this developmentally regulated gene, when fused upstream to the chloramphenicol acetyl transferase (CAT) reporter cassette was unable to direct significant CAT expression in wheat or tobacco suspension cells. Because this monocot gene promoter appeared to be under stringent tissue-specific control, a hybrid promoter approach using a nopaline synthase (nos) promoter was employed. A series of 3' deletions of the gliadin promoter were placed upstream of either a nonfunctional -101 nos or a nearly wild-type -155 nos promoter fused in turn to a CAT reporter gene cassette. Transient expression analysis of these plasmid DNAs in tobacco cells showed that the gliadin fragment could either restore the activity of the non-functional nos promoter (series I) or enhance the activity of the functional nos promoter (series II). The degree of restoration of the promoter function conferred by gliadin fragments of the first series was proportional to the enhancing effect of the same fragments in the second series of constructs. The transcriptional activity of the gliadin (-592 bp to -77 bp) -nos hybrid promoter was reduced by 26% upon 3' deletion of sequences in the region -141 bp to -77 bp, which contains both the TATA and CCAAT boxes.(ABSTRACT TRUNCATED AT 250 WORDS)