Identification of a second locus encoding β-amylase on chromosome 2 of barley

Differential expression of two β-amylase genes (Bmy1 and Bmy2) in developing and mature barley grain

Two barley (Hordeum vulgare L.) β-amylase genes (Bmy1 and Bmy2) were studied during the late maturation phase of grain development in four genotypes. The Bmy1 and Bmy2 DNA and amino acid sequences are extremely similar. The largest sequence differences are in the introns, seventh exon, and 3' UTR. Accumulation of Bmy2 mRNA was examined in developing grain at 17, 19, and 21 days after anthesis (DAA). One genotype, PI 296897, had significantly higher Bmy2 RNA transcript accumulation than the other three genotypes at all developmental stages. All four genotypes had Bmy2 mRNA levels decrease from 17 to 19 DAA, and remain the same from 19 to 21 DAA. Levels of Bmy1 mRNA were twenty thousand to over one hundred thousand times more than Bmy2 mRNA levels in genotypes Legacy, Harrington, and Ashqelon at all developmental stages and PI 296897 at 19 and 21 DAA. PI 296897 had five thousand times more Bmy1 mRNA than Bmy2 mRNA at 17 DAA. However, Bmy2 protein was not found at 17 DAA in any genotype. The presence of Bmy2 was immunologically detected at 19 DAA and was present in greater amounts at 21 DAA. Also, Bmy2 protein was found to be stored in mature grain and localized in the soluble fraction. However, Bmy1 protein was far more prevalent than Bmy2 at all developmental stages in all genotypes. Thus, the vast majority of β-amylase activity in developing and mature grain can be attributed to endosperm-specific β-amylase.

Structural and functional characterization of a winter malting barley

The development of winter malting barley (Hordeum vulgare L.) varieties is emerging as a worldwide priority due to the numerous advantages of these varieties over spring types. However, the complexity of both malting quality and winter hardiness phenotypes makes simultaneous improvement a challenge. To obtain an understanding of the relationship between loci controlling winter hardiness and malt quality and to assess the potential for breeding winter malting barley varieties, we structurally and functionally characterized the six-row accession "88Ab536", a cold-tolerant line with superior malting quality characteristics that derives from the cross of NE76129/Morex//Morex. We used 4,596 SNPs to construct the haplotype structure of 88Ab536 on which malting quality and winter hardiness loci reported in the literature were aligned. The genomic regions determining malting quality and winter hardiness traits have been defined in this founder germplasm, which will assist breeders in targeting regions for marker-assisted selection. The Barley1 GeneChip array was used to functionally characterize 88Ab536 during malting. Its gene expression profile was similar to that of the archetypical malting variety Morex, which is consistent with their similar malting quality characteristics. The characterization of 88Ab536 has increased our understanding of the genetic relationships of malting quality and winter hardiness, and will provide a genetic foundation for further development of more cold-tolerant varieties that have malt quality characteristics that meet or exceed current benchmarks.

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.

Mutants and duplication in chromosome 7 (syn. 5H) in the barley line HA21: duplications may enhance QTLs and serve to make constant linear cis-heterozygosity

Cytological and linkage data indicate a duplication in the short arm of chromosome 7 (syn. 5H) in the mutant line HA21 (barley, Hordeum vulgare, cv. 'Pirkka'). The associated mutant (ha21) shows a weighted average linkage of 22.1 cM with pld, hitherto an ignored anthocyaninless gene, of cv. Pirkka. Some crosses produce F2 segregants with an exaggerated ha21 phenotype which may represent position effect or increased dosage of the mutant gene through recombination. Compared with cv. Pirkka, HA21 has changes in grain chemistry (alpha- and beta-amylase, beta-glucanase), which may be caused by changed QTL dosage or QTL position effect due to duplication. The use of duplication in creating constant +m/+ m or m+/m+ linear cis-heterozygotes is suggested. Linear cis-heterozygotes may produce stable heterosis or attenuate the undesired effects of drastic mutants.

Allele-dependent barley grain beta-amylase activity

The wild ancestor of cultivated barley, Hordeum vulgare subsp. spontaneum (K. Koch) A. & Gr. (H. spontaneum), is a source of wide genetic diversity, including traits that are important for malting quality. A high beta-amylase trait was previously identified in H. spontaneum strains from Israel, and transferred into the backcross progeny of a cross with the domesticated barley cv Adorra. We have used Southern-blot analysis and beta-amy1 gene characterization to demonstrate that the high beta-amylase trait in the backcross line is co-inherited with the beta-amy1 gene from the H. spontaneum parent. We have analyzed the beta-amy1 gene organization in various domesticated and wild-type barley strains and identified three distinct beta-amy1 alleles. Two of these beta-amy1 alleles were present in modern barley, one of which was specifically found in good malting barley cultivars. The third allele, linked with high grain beta-amylase activity, was found only in a H. spontaneum strain from the Judean foothills in Israel. The sequences of three isolated beta-amy1 alleles are compared. The involvement of specific intron III sequences, in particular a 126-bp palindromic insertion, in the allele-dependent expression of beta-amylase activity in barley grain is proposed.

The distribution of RFLP markers on chromosome 2(2H) of barley in relation to the physical and genetic location of 5S rDNA

The 5S rDNA locus on the long arm of barley chromosome 2(2H) was genetically mapped in two crosses in relation to 30 other RFLP loci. Comparison of the genetic maps with the previously published physical position of the 5S rDNA, determined by in-situ hybridization, showed that there was a marked discrepancy between physical and genetic distance in both crosses, with recombination being less frequent in the proximal part of the arm. Pooled information from the present study and other published genetic maps showed that at least 26 of the 44 (59%) RFLPs that have been mapped on 2(2H)L lie distal to the 5S rDNA locus even though this region is only 27% of the physical length of the arm. The distribution of RFLP markers is significantly different from expected (P < 0.01), implying that the low-copy sequences used for RFLP analysis occur more frequently in distal regions of the arm and, or, that sequences in distal regions are more polymorphic.

The inheritance of β-amylase null in storage roots of sweet potato,Ipomoea batatas (L.) Lam

Several sweet potato genotypes were found to lack completely or to have only traces ofβ-amylase in their storage roots. Such genotypes do not increase in sweetness during cooking because, without a sufficient amount ofβ-amylase, the normal hydrolysis of starch to maltose does not occur in the cooking process. In order to study the inheritance of this biochemical variant in the genotype, 41 families were generated. The following conclusions were drawn from analyzing these families. (1) This trait is controlled by one recessive allele (designatedβ-amy) (2) It is inherited in a hexasomic or tetradisomic manner, but not disomically or tetrasomically. This conclusion supports previous cytological data that sweet potato is an autohexaploid or has two identical genomes plus one genome which is somewhat different. (3) Theβ-amy allele appears to exist at a high frequency in cultivated germplasm. (4) Breeding sweet potato for lowβ-amylase activity is relatively easy. New types of sweet potato without normalβ-amylase activity have great potential for processing and as a staple food.

Multiple molecular forms of β-amylase in seeds and vegetative tissues of barley

The molecular forms of β-amylase present in developing, mature, germinating and malted grains of barley (Hordeum vulgare L.), and in vegetative tissues, have been studied using Western-blot analyses and isoelectric focusing of isoenzymes. Five isoforms with different relative molecular masses (Mrs) could be recognised. The major isoform present in the mature grain, called isoform B, had an Mr of about 60 000. This was converted on malting or germination to two lower-Mr forms called C and D. Previous work (R. Lundgard and B. Svensson, 1986, Carlsberg Res. Commun. 51, 487-491) has shown that these result from partial proteolysis of isoform B. Isoenzyme analyses showed complex patterns of bands, with pIs between about 5.0 and 6.0. Two allelic types were present in the eight lines. A number of new bands with a range of pIs appeared during germination and malting.An isoform with the same Mr as D and a minor low-Mr isoform (E) were present in young developing whole caryopses (8-12 d after anthesis), but not in older developing endosperms (14-21 d after anthesis). Isoenzyme analyses also showed different patterns of bands in these two tissues, while hybrid-dot analyses indicated the presence of separate populations of mRNAs. It is suggested that the early endosperm isoforms (D and E) are "green" β-amylases present in the pericarp and-or testa of the young caryopses.Roots but not shoots or leaves also contained an isoform with the same Mr as D, although the pattern of isoenzymes differed from that present in the seed tissues.The fifth isoform, A, was a diffuse high-Mr form present in small amounts in all seed and vegetative tissues, and may correspond to a constitutively expressed form.These multiple molecular forms of β-amylase are discussed in relation to the recent report that β-amylase is encoded by two structural loci, with a total copy number of two to three per haploid genome (Kreis et al, 1988, Genet. Res. Camb. 51, 13-16).