Association mapping of malting quality traits in UK spring and winter barley cultivar collections

Historical malting quality data was collated from UK national and recommended list trial data and used in a GWAS. 25 QTL were identified, with the majority from spring barley cultivar sets. In Europe, the most economically significant use of barley is the production of malt for use in the brewing and distilling industries. As such, selection for traits related to malting quality is of great commercial interest. In order to study the genetic basis of variation for malting quality traits in UK cultivars, a historical set of trial data was collated from national and recommended list trials from the period 1988 to 2016. This data was used to estimate variety means for 20 quality related traits in 451 spring barley cultivars, and 407 winter cultivars. Genotypes for these cultivars were generated using iSelect 9k and 50k genotyping platforms, and a genome wide association scan performed to identify malting quality quantitative trait loci (QTL). 24 QTL were identified in spring barley cultivars, and 2 from the winter set. A number of these correspond to known malting quality related genes but the remainder represents novel genetic variation that is accessible to breeders for the genetic improvement of new cultivars.

Differences in hydrolytic enzyme activity accompany natural variation in mature aleurone morphology in barley (Hordeum vulgare L.)

The aleurone is a critical component of the cereal seed and is located at the periphery of the starchy endosperm. During germination, the aleurone is responsible for releasing hydrolytic enzymes that degrade cell wall polysaccharides and starch granules, which is a key requirement for barley malt production. Inter- and intra-species differences in aleurone layer number have been identified in the cereals but the significance of this variation during seed development and germination remains unclear. In this study, natural variation in mature aleurone features was examined in a panel of 33 Hordeum vulgare (barley) genotypes. Differences were identified in the number of aleurone cell layers, the transverse thickness of the aleurone and the proportion of aleurone relative to starchy endosperm. In addition, variation was identified in the activity of hydrolytic enzymes that are associated with germination. Notably, activity of the free fraction of β-amylase (BMY), but not the bound fraction, was increased at grain maturity in barley varieties possessing more aleurone. Laser capture microdissection (LCM) and transcriptional profiling confirmed that HvBMY1 is the most abundant BMY gene in developing grain and accumulates in the aleurone during early stages of grain fill. The results reveal a link between molecular pathways influencing early aleurone development and increased levels of free β-amylase enzyme, potentially highlighting the aleurone as a repository of free β-amylase at grain maturity.

Noncanonical interactions between serpin and β-amylase in barley grain improve β-amylase activity in vitro

Serpin protease inhibitors and β-amylase starch hydrolases are very abundant seed proteins in the endosperm of grasses. β-amylase is a crucial enzyme in the beer industry providing maltose for fermenting yeast. In animals and plants, inhibitory serpins form covalent linkages that inactivate their cognate proteases. Additionally, in animals, noninhibitory functions for serpins are observed such as metabolite carriers and chaperones. The function of serpins in seeds has yet to be unveiled. In developing endosperm, serpin Z4 and β-amylase showed similar in vivo spatio-temporal accumulation properties and colocalize in the cytosol of transformed tobacco leaves. A molecular interaction between recombinant proteins of serpin Z4 and β-amylase was revealed by surface plasmon resonance and microscale thermophoresis yielding a dissociation constant of 10-7 M. Importantly, the addition of serpin Z4 significantly changes β-amylase enzymatic properties by increasing its maximal catalytic velocity. The presence of serpin Z4 stabilizes β-amylase activity during heat treatment without affecting its critical denaturing temperature. Oxidative stress, simulated by the addition of CuCl2, leads to the formation of high molecular weight polymers of β-amylase similar to those detected in vivo. The polymers were cross-linked through disulfide bonds, the formation of which was repressed when serpin Z4 was present. The results suggest an unprecedented function for a plant seed serpin as a β-amylase-specific chaperone-like partner that could optimize β-amylase activity upon germination. This report is the first to describe a noninhibitory function for a serpin in plants.

Metabolite Profiling of Barley Grains Subjected to Water Stress: To Explain the Genotypic Difference in Drought-Induced Impacts on Malting Quality

Grain weight and protein content will be reduced and increased, respectively, when barley is subjected to water stress after anthesis, consequently deteriorating the malt quality. However, such adverse impact of water stress differs greatly among barley genotypes. In this study, two Tibetan wild barley accessions and two cultivated varieties differing in water stress tolerance were used to investigate the genotypic difference in metabolic profiles during grain-filling stage under drought condition. Totally, 71 differently accumulated metabolites were identified, including organic acids, amino acids/amines, and sugars/sugar alcohols. Their relative contents were significantly affected by water stress for all genotypes and differed distinctly between the wild and cultivated barleys. The principal component analysis of metabolites indicated that the Tibetan wild barley XZ147 possessed a unique response to water stress. When subjected to water stress, the wild barley XZ147 showed the most increase of β-amylase activity among the four genotypes, as a result of its higher lysine content, less indole-3-acetic acid (IAA) biosynthesis, more stable H2O2 homeostasis, and more up-regulation of BMY1 gene. On the other hand, XZ147 had the most reduction of β-glucan content under water stress than the other genotypes, which could be explained by the faster grain filling process and the less expression of β-glucan synthase gene GSL7. All these results indicated a great potential for XZ147 in barley breeding for improving water stress tolerance.

Association Mapping of Diastatic Power in UK Winter and Spring Barley by Exome Sequencing of Phenotypically Contrasting Variety Sets

Diastatic Power (DP) is an important quality trait for malt used in adjunct brewing and distilling. Substantial genetic variation for DP exists within UK elite barley cultivars, but breeding progress has been slow due to the limited demand, compared to the overall barley market, and difficulties in assessing DP. Estimates of DP (taken from recommended and national list trials between 1994 and 2012) from a collection of UK elite winter and spring varieties were used to identify contrasting sets of high and low DP varieties. DNA samples were pooled within sets and exome capture sequencing performed. Allele frequency estimates of Single Nucleotide Polymorphisms (SNPs) identified from the sequencing were used to identify genomic locations associated with differences in DP. Individual genotypes were generated from a set of custom KASP assays, both within sets and in a wider germplasm collection, to validate allele frequency estimates and marker associations with DP. QTL identified regions previously linked to variation in DP as well as novel associations. QTL colocalised with a number of genes annotated as having a diastase related function. Results indicate that winter barley is more genetically diverse for genes influencing DP. The marker assays produced by this work represent a resource that is available for immediate use by barley breeders in the production of new high DP varieties.

Differential RNA expression of Bmy1 during barley seed development and the association with β-amylase accumulation, activity, and total protein

The objective of this study was to determine if developing barley (Hordeum vulgare L.) seeds had differences in β-amylase 1 (Bmy1) mRNA accumulation, β-amylase (EC 3.2.1.2) activity, β-amylase protein accumulation, and total protein levels during late seed development from genotypes with different Bmy1 intron III alleles. Two North American malting barley cultivars (Hordeum vulgare ssp. vulgare) were chosen to represent the Bmy1.a and Bmy1.b alleles and, due to limited Bmy1 intron III allele variation in North American cultivars, two wild barleys (Hordeum vulgare ssp. spontaneum) were chosen to represent the Bmy1.c and Bmy1.d alleles. Wild barleys Ashqelon (Bmy1.c) and PI 296897 (Bmy1.d) had 2.5- to 3-fold higher Bmy1 mRNA levels than cultivars Legacy (Bmy1.a) and Harrington (Bmy1.b). Levels of Bmy1 mRNA were not significantly different between cultivated or between wild genotypes. In all four genotypes Bmy1 mRNA levels increased from 17 to 19 days after anthesis (DAA) and remained constant from 19 to 21 DAA. Ashqelon and PI 296897 had more β-amylase activity on a fresh weight basis than Legacy and Harrington at all developmental stages. β-Amylase protein levels increased from 17 DAA to maturity in all genotypes. Total protein in grains from wild genotypes was significantly higher than cultivated genotypes at all developmental stages. Higher levels of total protein in Ashqelon and PI 296897 could explain their higher levels of β-amylase activity, when expressed on a fresh weight basis. When β-amylase activities are expressed on a protein basis there are no statistical differences between the wild and cultivated barleys at maturity.

Comparative mapping of a QTL controlling black point formation in barley

The dark discoloration of the embryo end of barley grain (known as black point) is a physiological disorder and the discovery of a quantitative trait locus (QTL) on 2H confirms this trait is controlled genetically. The mechanisms underlying black point tolerance can now be dissected through identification of candidate genes. Comparisons between the QTL identified on chromosomes 2H of barley and 2B of wheat suggest that they are in similar positions near the centromere. In silico analysis, using rice, identified genes residing on two comparative chromosomes (4 and 7) of the rice genome. Analysis of the 12.6 Mb region revealed 1928 unique annotations classified into 11 functional categories. Expressed sequence tags (ESTs) with high sequence similarity to enzymes proposed to be involved in black point formation were used to develop restriction fragment length polymorphisms (RFLPs). To ensure an even coverage of markers across the QTL, RFLP markers were also developed from other ESTs. Mapping of these markers has reduced the QTL region from 28 to 18 cM. This study has identified candidate genes for the control of black point formation and paves the way for future research to develop black point resistant barley cultivars.

Genetic variation of Bmy1 alleles in barley (Hordeum vulgare L.) investigated by CAPS analysis

The enzyme beta-amylase is one of the most important hydrolytic enzymes in the grain of malting barley and is encoded by the gene Bmy1. To learn more about its structure and function, a total of 657 barley accessions including 541 Hordeum vulgare ssp. vulgare (HV), and 116 H. vulgare ssp. spontaneum (HS) were selected for the cleaved amplified polymorphic sequence (CAPS) analysis. These materials, covering all the 16 kinds of beta-amylase phenotypes screened from more than 8,500 accessions of the world barley germplasm, were classified into 13 CAPS types in the present study. A combined assay of phenotypes and CAPS types revealed extensive genetic variation at the Bmy1 locus, and in total 23 Bmy1 allele types were identified. The newly identified alleles (A-I-11, A-II-6, A-II-7, A-II-10, B-I-3, B-I-12 and B-I-13) provided us with a novel resource for barley breeding and Bmy1 study. In HV barley, six out of seven major allele types (C-II-1, B-II-2, B-Ia-3, A-II-5, A-II-6, and A-II-7) were shared with HS barley; the B-I-8 allele, which was predominant in north European cultivated barley, was found to be unique. Remarkably, very low Bmy1 genetic variation was detected in Tibetan barleys, which puts the validity of the hypothesis that Tibet is one of the original centers of cultivated barley into question.

The {beta}-amylase genes of grasses and a phylogenetic analysis of the Triticeae (Poaceae)

There are two forms of β-amylase in the Triticeae crop plants wheat, barley, and rye: an endosperm-specific form encoded by two or three closely linked genes, and a tissue-ubiquitous form encoded by a single gene. Both rice and corn have one ubiquitously expressed form encoded by a single gene. This study focuses on two phylogenetic analyses of β-amylase gene sequences. First, a phylogenetic analysis of coding sequences from wheat, barley, rye, rice, and corn was expected to clarify the relationship between the endosperm-specific and tissue-ubiquitous forms of the protein. Instead, it illustrates possible effects of distant outgroups, based on conflicting patterns of character state variation consistent with different root positions. Next, a broad sample of the monogenomic Triticeae was included in a phylogenetic analysis based on sequences from a portion of the tissue-ubiquitous β-amylase gene. The results were compared to existing Triticeae gene trees, among which extensive conflict had been noted in the past. One additional gene tree has not completely clarified the complexity of the group, but has shed additional light on reticulate phylogenetic patterns within the tribe, including relationships involving Eremopyrum, Thinopyrum, and the Triticum/Aegilops group.