Structure of the genes encoding Hordeum vulgare (1----3,1----4)-beta-glucanase isoenzymes I and II and functional analysis of their promoters in barley aleurone protoplasts

Quality attributes for barley malt: "The backbone of beer"

Malting is the process of preparing barley for brewing through partial germination followed by drying. This process softens the grain cell wall and stimulates the production of diastatic enzymes, which convert starch into malt extract. The suitability of a barley grain for malt production depends upon a large number of quality parameters that are crucial for the identification and release of high-quality malt varieties. Maintaining tight control of these quality attributes is essential to ensure high processing efficiency and final product quality in brewery and malt house. Therefore, we have summarized the basic malting process and various physiological and biochemical quality parameters that are desirable for better malt quality. This study may provide an understanding of the process, problems faced, and opportunities to maltsters and researchers to improve the malt efficiency by altering the malting process or malt varieties.

Discovering coherency of specific gene expression and optical reflectance properties of barley genotypes differing for resistance reactions against powdery mildew

Hyperspectral imaging has proved its potential for evaluating complex plant-pathogen interactions. However, a closer link of the spectral signatures and genotypic characteristics remains elusive. Here, we show relation between gene expression profiles and specific wavebands from reflectance during three barley-powdery mildew interactions. Significant synergistic effects between the hyperspectral signal and the corresponding gene activities has been shown using the linear discriminant analysis (LDA). Combining the data sets of hyperspectral signatures and gene expression profiles allowed a more precise differentiation of the three investigated barley-Bgh interactions independent from the time after inoculation. This shows significant synergistic effects between the hyperspectral signal and the corresponding gene activities. To analyze this coherency between spectral reflectance and seven different gene expression profiles, relevant wavelength bands and reflectance intensities for each gene were computed using the Relief algorithm. Instancing, xylanase activity was indicated by relevant wavelengths around 710 nm, which are characterized by leaf and cell structures. HvRuBisCO activity underlines relevant wavebands in the green and red range, elucidating the coherency of RuBisCO to the photosynthesis apparatus and in the NIR range due to the influence of RuBisCO on barley leaf cell development. These findings provide the first insights to links between gene expression and spectral reflectance that can be used for an efficient non-invasive phenotyping of plant resistance and enables new insights into plant-pathogen interactions.

Variation in barley (1 → 3, 1 → 4)-β-glucan endohydrolases reveals novel allozymes with increased thermostability

Novel barley (1 → 3, 1 → 4)-β-glucan endohydrolases with increased thermostability. Rapid and reliable degradation of (1 → 3, 1 → 4)-β-glucan to produce low viscosity wort is an essential requirement for malting barley. The (1 → 3, 1 → 4)-β-glucan endohyrolases are responsible for the primary hydrolysis of cell wall β-glucan. The variation in β-glucanase genes HvGlb1 and HvGlb2 that encode EI and EII, respectively, were examined in elite and exotic germplasm. Six EI and 14 EII allozymes were identified, and significant variation was found in β-glucanase from Hordeum vulgare ssp. spontaneum (wild barley), the progenitor of modern cultivated barley. Allozymes were examined using prediction methods; the change in Gibbs free energy of the identified amino acid substitutions to predict changes in enzyme stability and homology modelling to examine the structure of the novel allozymes using the existing solved EII structure. Two EI and four EII allozymes in wild barley accessions were predicted to have improved barley β-glucanase thermostability. One novel EII candidate was identified in existing backcross lines with contrasting HvGlb2 alleles from wild barley and cv Flagship. The contrasting alleles in selected near isogenic lines were examined in β-glucanase thermostability analyses. The EII from wild barley exhibited a significant increase in β-glucanase thermostability conferred by the novel HvGlb2 allele. Increased β-glucanase thermostability is heritable and candidates identified in wild barley could improve malting and brewing quality in new varieties.

From analysis of mutants to genetic engineering

This chapter describes the research of developing transgenic barley for synthesis of recombinant proteins with practical significance and of metabolic engineering of proanthocyanidin-free barley. The results were obtained by graduate students, postdoctoral researchers, and visiting scientists at the Carlsberg Laboratory from 1972-1996 and during the past ten years at Washington State University. It is written in appreciation of their enthusiasm, skill, and perseverance.

A role for the DOF transcription factor BPBF in the regulation of gibberellin-responsive genes in barley aleurone

Functional analyses of a number of hydrolase gene promoters, induced by gibberellin (GA) in aleurone cells following germination, have identified a GA-responsive complex as a tripartite element containing a pyrimidine box motif 5'-CCTTTT-3'. We describe here that BPBF, a barley (Hordeum vulgare) transcription factor of the DOF (DNA-Binding with One Finger) class, previously shown to be an activator of reserve protein encoding genes during development, also has a role in the control of hydrolase genes following seed germination. Northern-blot, reverse transcriptase-polymerase chain reaction, and in situ hybridization analyses evidenced that the transcripts of the BPBF-encoding gene (Pbf), besides being present during endosperm development, are also expressed in aleurone cells of germinated seeds where they are induced by GA, an effect counteracted by abscisic acid. Electrophoretic mobility shift assays have shown that the BPBF protein binds specifically to the pyrimidine box motif in vitro within the different sequence contexts that naturally occur in the promoters of genes encoding a cathepsin B-like protease (Al21) and a low-isoelectric point alpha-amylase (Amy2/32b), both induced in the aleurone layers in response to GA. In transient expression experiments, BPBF repressed transcription of the Al21 promoter in GA-treated barley aleurone layers and reverted the GAMYB-mediated activation of this protease promoter.

Molecular and physical mapping of a barley gene on chromosome arm 1 HL that causes sterility in hybrids with wheat

Addition of the long arm of barley chromosome 1H (1HL) to wheat causes severe meiotic abnormalities and complete sterility of the plants. To map the barley gene responsible for the 1H-induced sterility of wheat, a series of addition lines of translocated 1H chromosomes were developed from the crosses between the wheat 'Shinchunaga' and five reciprocal translocation lines derived from the barley line St.13559. Examination of the seed fertility of the addition lines revealed that the sterility gene is located in the interstitial 25% region of the 1HL arm. The genetic location of the sterility gene was also estimated by physically mapping sequence-tagged site (STS) markers and simple-sequence repeat (SSR) markers with known map locations. The sterility gene is designated Shw (sterility in hybrids with wheat). Comparison of the present physical map of 1HL with two previously published genetic maps revealed a paucity of markers in the proximal 30% region and non-random distribution of SSR markers. Two inconsistencies in marker order were found between the present physical map and the consensus genetic map of group 1 chromosomes of Triticeae. On the basis of the effects on meiosis and chromosomal location, the relationship of the present sterility gene with other fertility-related genes of Triticeae is discussed.

A novel type of arabinoxylan arabinofuranohydrolase isolated from germinated barley analysis of substrate preference and specificity by nano-probe NMR

An arabinoxylan arabinofuranohydrolase was isolated from barley malt. The enzyme preparation, Ara 1, contained two polypeptides with apparent molecular masses of approximately 60 and approximately 66 kDa, a pI of 4.55 and almost identical N-terminal amino-acid sequences. With p-nitrophenyl alpha-L-arabinofuranoside (pNPA) as substrate, Ara 1 exhibited a Km of 0.5 mM and a Vmax of 6.7 micromol. min-1.(mg of protein)-1. Maximum activity was displayed at pH 4.2 and 60 degrees C, and, under these conditions, the half-life of the enzyme was 8 min. The Ara 1 preparation showed no activity against p-nitrophenyl alpha-L-arabinopyranoside or p-nitrophenyl beta-D-xylopyranoside. Substrate preference and specificity were investigated using pure oligosaccharides and analysis by TLC and nano-probe NMR. Ara 1 released arabinose from high-molecular-mass arabinoxylan and arabinoxylan-derived oligosaccharides but was inactive against linear or branched-chain arabinan. Arabinose was readily released from both singly and doubly substituted xylo-oligosaccharides. Whereas single 2-O-linked and 3-O-linked arabinose substituents on non-reducing terminal xylose were released at similar rates, there was a clear preference for 2-O-linked arabinose on internal xylose residues. When Ara 1 acted on oligosaccharides with doubly substituted, non-reducing terminal xylose, the 3-O-linked arabinose group was preferred as the initial point of attack. Oligosaccharides with doubly substituted internal xylose were poor substrates and no preference could be determined. The enzyme described here is the first reported arabinoxylan arabinofuranohydrolase which is able to release arabinose from both singly and doubly substituted xylose, and it hydrolyses p-nitrophenyl alpha-L-arabinofuranoside at a rate similar to that observed for oligosaccharide substrates.

Cloning and characterization of a gibberellin-induced RNase expressed in barley aleurone cells

We cloned a cDNA for a gibberellin-induced ribonuclease (RNase) expressed in barley (Hordeum vulgare) aleurone and the gene for a second barley RNase expressed in leaf tissue. The protein encoded by the cDNA is unique among RNases described to date in that it contains a novel 23-amino acid insert between the C2 and C3 conserved sequences. Expression of the recombinant protein in tobacco (Nicotiana tabacum) suspension-cultured protoplasts gave an active RNase of the expected size, confirming the enzymatic activity of the protein. Analyses of hormone regulation of expression of mRNA for the aleurone RNase revealed that, like the pattern for alpha-amylase, mRNA levels increased in the presence of gibberellic acid, and its antagonist abscisic acid prevented this effect. Quantitative studies at early times demonstrated that cycloheximide treatment of aleurone layers increased mRNA levels 4-fold, whereas a combination of gibberellin plus cycloheximide treatment was required to increase alpha-amylase mRNA levels to the same extent. These results are consistent with loss of repression as an initial effect of gibberellic acid on transcription of those genes, although the regulatory pathways for the two genes may differ.

Target genes and regulatory domains of the GAMYB transcriptional activator in cereal aleurone

GAMYB is an MYB transcription factor which is expressed in cereal aleurone cells in response to gibberellin (GA). HvGAMYB binds to the TAACAAA box of a high-pl alpha-amylase gene promoter and transcriptionally activates its expression. In this study, we examined the role of HvGAMYB in activating expression of other GA-regulated genes encoding hydrolytic enzymes. In transient expression experiments, HvGAMYB transactivated expression of reporter genes fused to a low-pl alpha-amylase gene promoter, an EII (1-3, 1-4)-beta-glucanase gene promoter and a cathepsin B-like protease promoter. HvGAMYB DNA binding specificity was determined using a PCR-based random site selection using HvGAMYB fusion protein isolated from E. coli. The deduced consensus closely resembled gibberellin response elements in alpha-amylase promoters. Functional analysis of HvGAMYB by transient expression of C terminal HvGAMYB deletions in barley aleurone cells identified two transcriptional activation domains (TADs) which function in transcriptional regulation of both high- and low-pl alpha-amylase promoters. The same TADs were identified using a heterologous yeast expression system. Together, these results indicate that HvGAMYB has two TADs. These domains are C-terminal to its DNA-binding domain.

Transgenic barley expressing a protein-engineered, thermostable (1,3-1,4)-beta-glucanase during germination

The codon usage of a hybrid bacterial gene encoding a thermostable (1,3-1,4)-beta-glucanase was modified to match that of the barley (1,3-1,4)-beta-glucanase isoenzyme EII gene. Both the modified and unmodified bacterial genes were fused to a DNA segment encoding the barley high-pI alpha-amylase signal peptide downstream of the barley (1,3-1,4)-beta-glucanase isoenzyme EII gene promoter. When introduced into barley aleurone protoplasts, the bacterial gene with adapted codon usage directed synthesis of heat stable (1,3-1,4)-beta-glucanase, whereas activity of the heterologous enzyme was not detectable when protoplasts were transfected with the unmodified gene. In a different expression plasmid, the codon modified bacterial gene was cloned downstream of the barley high-pI alpha-amylase gene promoter and signal peptide coding region. This expression cassette was introduced into immature barley embryos together with plasmids carrying the bar and the uidA genes. Green, fertile plants were regenerated and approximately 75% of grains harvested from primary transformants synthesized thermostable (1,3-1,4)-beta-glucanase during germination. All three trans genes were detected in 17 progenies from a homozygous T1 plant.

The barley Hooded mutation caused by a duplication in a homeobox gene intron

In barley (Hordeum vulgare L.) the unit of inflorescence is the spikelet, which bears a fertile bract, the lemma, and the floret consisting of palea, two lodicules, three stamens and the pistil. The Hooded mutation causes the appearance of an extra flower of inverse polarity on the lemma. This phenotype is governed by the single dominant genetic locus K3. Here we show that the homeobox gene Knox3 represents this locus. Ectopic Knox3 gene expression in the primordium of the extra floret is caused by a 305-base pair duplication in intron 4, and phenocopies of the mutation are obtained in the heterologous tobacco system by Knox3 overexpression. It is concluded that homeotic genes of the Knox gene family are involved in floral evocation. Furthermore, the study of polarity of reproductive organs in K and related mutants can now focus on homeobox genes.

Structure and expression of a barley acidic beta-glucanase gene

A barley acidic beta-1,3-glucanase gene was recovered from a barley genomic library by homology with a partial cDNA of barley basic beta-1,3-glucanase isoenzyme GII. The gene, Abg2, is homologous to the PR2 family of pathogenesis-related beta-1,3-glucanase genes. The ABG2 protein has 81% amino acid similarity to barley basic beta-1,3-glucanase GII. The ABG2 protein is encoded as a preprotein of 336 amino acids including a 28 amino acid signal peptide. A 299 bp intron occurs within codon 25. The mature ABG2 protein has a predicted mass of 32,642 Da and a calculated isoelectric point of 4.9. The second exon of the Abg2 gene shows a strong preference for G + C in the third position of degenerate codons. The Abg2 gene was functionally expressed in Escherichia coli. Abg2 mRNA is constitutively expressed in barley root; leaf expression of Abg2 mRNA is induced by mercuric chloride and infection by Erysiphe graminis f. sp. hordei. Southern blot analysis indicates that Abg2 is a member of a small gene family.