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Flowering plants with indeterminate inflorescences often produce more floral structures than they require. We found that floral primordia initiations in barley ( Hordeum vulgare L.) are molecularly decoupled from their maturation into grains. While initiation is dominated by flowering-time genes, floral growth is specified by light signaling, chloroplast, and vascular developmental programs orchestrated by barley CCT MOTIF FAMILY 4 ( HvCMF4 ), which is expressed in the inflorescence vasculature. Consequently, mutations in HvCMF4 increase primordia death and pollination failure, mainly through reducing rachis greening and limiting plastidial energy supply to developing heterotrophic floral tissues. We propose that HvCMF4 is a sensory factor for light that acts in connection with the vascular-localized circadian clock to coordinate floral initiation and survival. Notably, stacking beneficial alleles for both primordia number and survival provides positive implications on grain production. Our findings provide insights into the molecular underpinnings of grain number determination in cereal crops.

Grasses have varying inflorescence shapes; however, little is known about the genetic mechanisms specifying such shapes among tribes. Here, we identify the grass-specific TCP transcription factor COMPOSITUM 1 (COM1) expressing in inflorescence meristematic boundaries of different grasses. COM1 specifies branch-inhibition in barley (Triticeae) versus branch-formation in non-Triticeae grasses. Analyses of cell size, cell walls and transcripts reveal barley COM1 regulates cell growth, thereby affecting cell wall properties and signaling specifically in meristematic boundaries to establish identity of adjacent meristems. COM1 acts upstream of the boundary gene Liguleless1 and confers meristem identity partially independent of the COM2 pathway. Furthermore, COM1 is subject to purifying natural selection, thereby contributing to specification of the spike inflorescence shape. This meristem identity pathway has conceptual implications for both inflorescence evolution and molecular breeding in Triticeae., Grasses have diverse inflorescence morphologies, but the underlying genetic mechanisms are unclear. Here, the authors report a TCP transcription factor COM1 affects cell growth through regulation of cell wall properties and promotes branch formation in non-Triticeae grasses but branch inhibition in barley (Triticeae).

Grasses have varying inflorescence shapes; however, little is known about the genetic mechanisms specifying such shapes among tribes. We identified the grass-specific TCP transcription factor COMPOSITUM 1 (COM1) expressed in inflorescence meristematic boundaries of different grasses. COM1 specifies branch-inhibition in Triticeae (barley) versus branch-formation in non-Triticeae grasses. Analyses of cell size, cell walls and transcripts revealed barley COM1 regulates cell growth, affecting cell wall properties and signaling specifically in meristematic boundaries to establish identity of adjacent meristems.COM1acts upstream of the boundary geneLiguleless1and confers meristem identity partially independent of theCOM2pathway. Furthermore, COM1 is subject to purifying natural selection, thereby contributing to specification of the spike inflorescence shape. This meristem identity pathway has conceptual implications for both inflorescence evolution and molecular breeding in Triticeae.

Increasing grain yield is an endless challenge for cereal crop breeding. In barley (Hordeum vulgare), grain number is controlled mainly by Six-rowed spike 1 (Vrs1), which encodes a homeodomain leucine zipper class I transcription factor. However, little is known about the genetic basis of grain size. Here, we show that extreme suppression of lateral florets contributes to enlarged grains in deficiens barley. Through a combination of fine-mapping and resequencing of deficiens mutants, we have identified that a single amino acid substitution at a putative phosphorylation site in VRS1 is responsible for the deficiens phenotype. deficiens mutant alleles confer an increase in grain size, a reduction in plant height, and a significant increase in thousand grain weight in contemporary cultivated germplasm. Haplotype analysis revealed that barley carrying the deficiens allele (Vrs1.t1) originated from two-rowed types carrying the Vrs1.b2 allele, predominantly found in germplasm from northern Africa. In situ hybridization of histone H4, a marker for cell cycle or proliferation, showed weaker expression in the lateral spikelets compared with central spikelets in deficiens. Transcriptome analysis revealed that a number of histone superfamily genes were up-regulated in the deficiens mutant, suggesting that enhanced cell proliferation in the central spikelet may contribute to larger grains. Our data suggest that grain yield can be improved by suppressing the development of specific organs that are not positively involved in sink/source relationships.

Background Short-culm mutants have been widely used in breeding programs to increase lodging resistance. In barley (Hordeum vulgare L.), several hundreds of short-culm mutants have been isolated over the years. The objective of the present study was to identify the Brachytic1 (Brh1) semi-dwarfing gene and to test its effect on yield and malting quality. Results Double-haploid lines generated through a cross between a brh1.a mutant and the European elite malting cultivar Quench, showed good malting quality but a decrease in yield. Especially the activities of the starch degrading enzymes β-amylase and free limit dextrinase were high. A syntenic approach comparing markers in barley to those in rice (Oryza sativa L.), sorghum (Sorghum bicolor Moench) and brachypodium (Brachypodium distachyon P. Beauv) helped us to identify Brh1 as an orthologue of rice D1 encoding the Gα subunit of a heterotrimeric G protein. We demonstrated that Brh1 is allelic to Ari-m. Sixteen different mutant alleles were described at the DNA level. Conclusions Mutants in the Brh1 locus are deficient in the Gα subunit of a heterotrimeric G protein, which shows that heterotrimeric G proteins are important regulators of culm length in barley. Mutant alleles do not have any major negative effects on malting quality.

In 1928, the Swedish geneticists Hermann Nilsson-Ehle and Åke Gustafsson started on their suggestion experiments with induced mutations using the barley crop. In 1953, at the instigation of the Swedish Government, the 'Group for Theoretical and Applied Mutation Research' was established. Its aim was to study basic research problems in order to influence and improve methods for breeding cultivated plants. The research was non-commercial, even if some mutants were of practical importance. The peaks of activities occurred during the 1950s, 1960s and 1970s. Applying X-rays and UV-irradiation very soon the first chlorophyll mutations were obtained followed by the first viable mutations 'Erectoides'. Soon the X-ray experiments expanded with other types of irradiation such as neutrons etc. and finally with chemical mutagens, starting with mustard gas and concluding with the sodium azide. The research brought a wealth of observations of general biological importance, high increased mutation frequencies, difference in the mutation spectrum and to direct mutagenesis for specific genes. A rather large collection of morphological and physiological mutations, about 12 000 different mutant alleles, with a very broad variation were collected and incorporated into the Nordic Genetic Resource Center (NordGen) Sweden. Barley, the main experimental crop has become one of the few higher plants in which biochemical genetics and molecular biological studies are now feasible. The collection is an outstanding material for mapping genes and investigating the barley genome. Several characters have been studied and analyzed in more detail and are presented in this historical review.

The hydrophobic cuticle covers the surface of the most aerial organs of land plants. The barley mutant eceriferum‐zv (cer‐zv), which is hypersensitive to drought, is unable to accumulate a sufficient quantity of cutin in its leaf cuticle. The mutated locus has been mapped to a 0.02 cM segment in the pericentromeric region of chromosome 4H. As a map‐based cloning approach to isolate the gene was therefore considered unlikely to be feasible, a comparison was instead made between the transcriptomes of the mutant and the wild type. In conjunction with extant genomic information, on the basis of predicted functionality, only two genes were considered likely to encode a product associated with cutin formation. When eight independent cer‐zv mutant alleles were resequenced with respect to the two candidate genes, it was confirmed that the gene underlying the mutation in each allele encodes a Gly‐Asp‐Ser‐Leu (GDSL)‐motif esterase/acyltransferase/lipase. The gene was transcribed in the epidermis, and its product was exclusively deposited in cell wall at the boundary of the cuticle in the leaf elongation zone, coinciding with the major site of cutin deposition. CER‐ZV is speculated to function in the deposition of cutin polymer. Its homologs were found in green algae, moss, and euphyllophytes, indicating that it is highly conserved in plant kingdom., Via genetic mapping and comparative transcriptomics, we identified a GDSL‐motif esterase/acyltransferase/lipase gene that was associated with cutin formation and leaf water retention in barley.

Reduced plant height and culm robustness are quantitative characteristics important for assuring cereal crop yield and quality under adverse weather conditions. A very limited number of short-culm mutant alleles were introduced into commercial crop cultivars during the Green Revolution. We identified phenotypic traits, including sturdy culm, specific for deficiencies in brassinosteroid biosynthesis and signaling in semidwarf mutants of barley (Hordeum vulgare). This set of characteristic traits was explored to perform a phenotypic screen of near-isogenic short-culm mutant lines from the brachytic, breviaristatum, dense spike, erectoides, semibrachytic, semidwarf, and slender dwarf mutant groups. In silico mapping of brassinosteroid-related genes in the barley genome in combination with sequencing of barley mutant lines assigned more than 20 historic mutants to three brassinosteroid-biosynthesis genes (BRASSINOSTEROID-6-OXIDASE, CONSTITUTIVE PHOTOMORPHOGENIC DWARF, and DIMINUTO) and one brassinosteroid-signaling gene (BRASSINOSTEROID-INSENSITIVE1 [HvBRI1]). Analyses of F2 and M2 populations, allelic crosses, and modeling of nonsynonymous amino acid exchanges in protein crystal structures gave a further understanding of the control of barley plant architecture and sturdiness by brassinosteroid-related genes. Alternatives to the widely used but highly temperature-sensitive uzu1.a allele of HvBRI1 represent potential genetic building blocks for breeding strategies with sturdy and climate-tolerant barley cultivars.

Inflorescence architecture of barley ( Hordeum vulgare L.) is common among the Triticeae species, which bear one to three single-flowered spikelets at each rachis internode. Triple spikelet meristem is one of the unique features of barley spikes, in which three spikelets (one central and two lateral spikelets) are produced at each rachis internode. Fertility of the lateral spikelets at triple spikelet meristem gives row-type identity to barley spikes. Six-rowed spikes show fertile lateral spikelets and produce increased grain yield per spike, compared with two-rowed spikes with sterile lateral spikelets. Thus, far, two loci governing the row-type phenotype were isolated in barley that include Six-rowed spike1 ( Vrs1 ) and Intermedium-C . In the present study, we isolated Six-rowed spike4 ( Vrs4 ), a barley ortholog of the maize ( Zea mays L.) inflorescence architecture gene RAMOSA2 ( RA2 ). Eighteen coding mutations in barley RA2 ( HvRA2 ) were specifically associated with lateral spikelet fertility and loss of spikelet determinacy. Expression analyses through mRNA in situ hybridization and microarray showed that Vrs4 ( HvRA2 ) controls the row-type pathway through Vrs1 ( HvHox1 ), a negative regulator of lateral spikelet fertility in barley. Moreover, Vrs4 may also regulate transcripts of barley SISTER OF RAMOSA3 ( HvSRA ), a putative trehalose-6-phosphate phosphatase involved in trehalose-6-phosphate homeostasis implicated to control spikelet determinacy. Our expression data illustrated that, although RA2 is conserved among different grass species, its down-stream target genes appear to be modified in barley and possibly other species of tribe Triticeae.

The barley (Hordeum vulgare L.) mutant erectoides-k.32 (ert-k.32) was isolated in 1947 from an X-ray-mutant population of cultivar ‘Bonus’. The mutant was released as a cultivar in 1958 with the name ‘Pallas’ – one of the first cereal crop cultivars developed from induced mutants. ‘Pallas’ is a semi-dwarf barley cultivar known for its culm stability and resistance to lodging. In total, eight allelic ert-k mutants are known that show different phenotypic strength concerning culm length and spike architecture. They represent alternatives to the widely used, but pleiotropic ‘Green Revolution’ alleles of the Sdw1 (semidwarf1/denso) and Uzu1 (semi-brachytic1) genes in breeding of robust elite barley cultivars. In the present study, we locate Ert-k to a 15.7-cM region in the centromeric region of chromosome 6H. Although the interval is estimated to contain approximately 700 genes, the work provides a solid foundation for the identification of the underlying mutations causing the ert-k lodging-resistant phenotype. In addition, the linked markers could be used to follow the ert-k mutant genotype in marker-assisted selection of new lodging-resistant barley cultivars.

Plant architecture has clear agronomic and economic implications for crops such as wheat and barley, as it is a critical factor for determining grain yield. Despite this, only limited molecular information is available about how grain-bearing inflorescences, called spikes, are formed and maintain their regular, distichous pattern. Here we elucidate the molecular and hormonal role of Six-rowed spike 2 (Vrs2), which encodes a SHORT INTERNODES (SHI) transcriptional regulator during barley inflorescence and shoot development. We show that Vrs2 is specifically involved in floral organ patterning and phase duration by maintaining hormonal homeostasis and gradients during normal spike development and similarly influences plant stature traits. Furthermore, we establish a link between the SHI protein family and sucrose metabolism during organ growth and development that may have implications for deeper molecular insights into inflorescence and plant architecture in crops.

The awn, an apical extension from the lemma of the spikelet, plays important roles in seed dispersal, burial, and photosynthesis. Barley typically has long awns, but short-awn variants exist. The short awn 2 (lks2) gene, which produces awns about 50% shorter than normal, is a natural variant that is restricted to Eastern Asia. Positional cloning revealed that Lks2 encodes a SHI-family transcription factor. Allelism tests showed that lks2 is allelic to unbranched style 4 (ubs4) and breviaristatum-d (ari-d), for which the phenotypes are very short awn and sparse stigma hairs. The gene identity was validated by 25 mutant alleles with lesions in the Lks2 gene. Of these, 17 affected either or both conserved regions: the zinc-binding RING-finger motif and the IGGH domain. Lks2 is highly expressed in awns and pistils. Histological observations of longitudinal awn sections showed that the lks2 short-awn phenotype resulted from reduced cell number. Natural variants of lks2 were classified into three types, but all shared a single-nucleotide polymorphism (SNP) that causes a proline-to-leucine change at position 245 in the IGGH domain. All three lks2 natural variants were regarded as weak alleles because their awn and pistil phenotypes are mild compared with those of the 25 mutant alleles. Natural variants of lks2 found in the east of China and the Himalayas had considerably different sequences in the regions flanking the critical SNP, suggesting independent origins. The available results suggest that the lks2 allele might have a selective advantage in the adaptation of barley to high-precipitation areas of Eastern Asia.

A typical barley (Hordeum vulgare) floret consists of reproductive organs three stamens and a pistil, and non-reproductive organs-lodicules and two floral bracts, abaxial called 'lemma' and adaxial 'palea'. The floret is subtended by two additional bracts called outer or empty glumes. Together these organs form the basic structural unit of the grass inflorescence, a spikelet. There are commonly three spikelets at each rachis (floral stem of the barley spike) node, one central and two lateral spikelets. Rare naturally occurring or induced phenotypic variants that contain a third bract subtending the central spikelets have been described in barley. The gene responsible for this phenotype was called the THIRD OUTER GLUME1 (Trd1). The Trd1 mutants fail to suppress bract growth and as a result produce leaf-like structures that subtend each rachis node in the basal portion of the spike. Also, floral development at the collar is not always suppressed. In rice and maize, recessive mutations in NECK LEAF1 (Nl1) and TASSEL SHEATH1 (Tsh1) genes, respectively, have been shown to be responsible for orthologous phenotypes. Fine mapping of the trd1 phenotype in an F(3) recombinant population enabled us to position Trd1 on the long arm of chromosome 1H to a 10 cM region. We anchored this to a conserved syntenic region on rice chromosome Os05 and selected a set of candidate genes for validation by resequencing PCR amplicons from a series of independent mutant alleles. This analysis revealed that a GATA transcription factor, recently proposed to be Trd1, contained mutations in 10 out of 14 independent trd1 mutant alleles that would generate non-functional TRD1 proteins. Together with genetic linkage data, we confirm the identity of Trd1 as the GATA transcription factor ortholog of rice Nl1 and maize Tsh1 genes.

Time to flowering has an important impact on yield and has been a key trait in the domestication of crop plants and the spread of agriculture. In 1961, the cultivar Mari ( mat-a.8 ) was the very first induced early barley ( Hordeum vulgare L.) mutant to be released into commercial production. Mari extended the range of two-row spring barley cultivation as a result of its photoperiod insensitivity. Since its release, Mari or its derivatives have been used extensively across the world to facilitate short-season adaptation and further geographic range extension. By exploiting an extended historical collection of early-flowering mutants of barley, we identified Praematurum-a ( Mat-a ), the gene responsible for this key adaptive phenotype, as a homolog of the Arabidopsis thaliana circadian clock regulator Early Flowering 3 ( Elf3 ). We characterized 87 induced mat-a mutant lines and identified >20 different mat-a alleles that had clear mutations leading to a defective putative ELF3 protein. Expression analysis of HvElf3 and Gigantea in mutant and wild-type plants demonstrated that mat-a mutations disturb the flowering pathway, leading to the early phenotype. Alleles of Mat-a therefore have important and demonstrated breeding value in barley but probably also in many other day-length-sensitive crop plants, where they may tune adaptation to different geographic regions and climatic conditions, a critical issue in times of global warming.

Since the early 20th century, barley (Hordeum vulgare) has been a model for investigating the effects of physical and chemical mutagens and for exploring the potential of mutation breeding in crop improvement. As a consequence, extensive and well-characterized collections of morphological and developmental mutants have been assembled that represent a valuable resource for exploring a wide range of complex and fundamental biological processes. We constructed a collection of 881 backcrossed lines containing mutant alleles that induce a majority of the morphological and developmental variation described in this species. After genotyping these lines with up to 3,072 single nucleotide polymorphisms, comparison to their recurrent parent defined the genetic location of 426 mutant alleles to chromosomal segments, each representing on average

The identification of genes underlying complex quantitative traits such as grain yield by means of conventional genetic analysis (positional cloning) requires the development of several large mapping populations. However, it is possible that phenotypically related, but more extreme, allelic variants generated by mutational studies could provide a means for more efficient cloning of QTLs (quantitative trait loci). In barley (Hordeum vulgare), with the development of high-throughput genome analysis tools, efficient genome-wide identification of genetic loci harbouring mutant alleles has recently become possible. Genotypic data from NILs (near-isogenic lines) that carry induced or natural variants of genes that control aspects of plant development can be compared with the location of QTLs to potentially identify candidate genes for development­-related traits such as grain yield. As yield itself can be divided into a number of allometric component traits such as tillers per plant, kernels per spike and kernel size, mutant alleles that both affect these traits and are located within the confidence intervals for major yield QTLs may represent extreme variants of the underlying genes. In addition, the development of detailed comparative genomic models based on the alignment of a high-density barley gene map with the rice and sorghum physical maps, has enabled an informed prioritization of ‘known function’ genes as candidates for both QTLs and induced mutant genes.

Genetic effects of ionizing radiations and chemical mutagens, especially with regard to the induction of viable mutants, were compared in barley. The chief mutagens used consisted of neutron and x irradiation, as well as treatments with glycidol, ethyleneimine, and ethyl methanesulfonate. Greenhouse mutants (chlorophyll mutants) amounted to 4000 cases in the years l958-l960. Field aberrations consisted of 2400 chlorophyll mutants, 650 dwarfs and other lethals, 5200 cases of so-called translocation sterility, and more than I000 cases of viable mutants. The total sum of X/sub 2/ aberrations, analyzed in the field, was 9300, in circa 2l500 spike progenies. Neutrons and x rays generally produce rates of greenhouse mutations up to 8 or 10%, or under special experimental con ditions up to 13 or 14%. Using ethyleneimine, rates of 25 to 30% are reached and with ethyl methanesulfonate, rates of 50 to 60%. The ratios of offspring showing translocation sterility to offspring with viable mutants are high applying neutrons and x rays, but low applying ethyleneimine and ethylmethanesulfonate. Ethyleneimine is especially efficient in inducing rare morphological mutants. In general, viable mutants are followed to the X/sub 3/ generation, Problems relating to the capacity of radiations and chemicals in causing specific gene mutationsmore » are briefly discussed. (P.C.H.)« less

Short-awned (breviaristatum) mutants were induced in the barley varieties Bonus, Foma and Kristina by ionizing radiations (X- and γ-rays, neutrons) and by chemical mutagens (chiefly sulfonates and ethyleneimine) About 260 mutants were isolated and certified in 1953–1972. Of those tested for allelism approximately 140 were distributed into 17 loci represented by 2 to 26 allelic mutants. Two loci have a single allele. The skew distribution of mutants at different loci is evident. Mutation rates and proportions were determined in M2 progenies during four years of screening. Chlorophyll mutations were approximately 25 times more frequent than breviaristatum types. Among the morphological mutants, erectoides, eceriferum and breviaristaturn types were approximately equally common. In general, chemical mutagens were 2–3 times more efficient than radiations in the induction of all kinds of mutation. Differences in detectability of mutant groups depending on parent variety are briefly discussed. A brief phenotypical description of the individual breviaristatum (ari) loci is given, illustrating the pleiotropic effects often found. Mutants in loci ari-a, -c, -d, -e, which have previously been placed on the chromosome map, may serve as good marker genes. Mutants of loci ari-1 and -m are of some practical interest owing to their stiff short straw and prolific spikes.

A multidimensional model useful in selection experiments involving mutant materials is described. A number of quantitative variables are combined to one single synthetic variable reflecting positive qualities of the original variables. The technique employed is related to mean square orthogonal regression. The obtained positive results are partially due to fortuitous data in the specific case analysed, pertaining to mutant selections in Svalov's Foma barley, cultivated at Riso (Denmark). The synthetic device has been further utilized in multidimensional analyses of phytotron-cultivated barley materials.

Homozygous intermedium mutations from two-row barley are generally characterized by their lateral florets being of increased size and fertility. Median florets develop normally. Sixty allelism-tested intermedium mutations represent nine different gene loci, each locus possessing a particular type of lateral floret development. The intermedium character is usually recessive. Two cases of dominant mutations have been recorded. The F2 generation of certain loci primarily give rise to double-recessive hexastichon plants (for instance int-c x int-d). Other locus combinations give rise, in individual progenies, to double-recessive hexastichon or irregular and deformed F2 plants (for instance int-a x int-c), and others, finally, produce double-recessive irregular and deformed F2 plants exclusively and no hexastichons (for instance int-a x int-e). Hexastichon types, consequently, may arise in two ways: (1) by direct mutation in the two-row locus of distichon types (Vv), and (2) as double-recessives in the second generation of hybrid combinations of special intermedium loci and alleles.

Lundqvist, U. and Lundqvist, A. 1990. Progressive promotion of lateral floret development in three- and four-gene combinations of intermedium genes in barley. —Hereditas 113: 237–242. Lund. Sweden. ISSK 00 18–0661. Received September 19. 1990. Accepted October 4, 1990 Gene interaction promoting laterai floret development in barley was studied in a total of 220 F3 families from prominent F2-plants selected in three- and four-gene segregations derived from double mutant constellations of intermedium genes combined in crosses. The study was based on 4 independently inherited loci, the three recessive int-a. int-c, and int-e, and the semidominant Int-d. Three-gene F2-segregations. totally 17, were based on the 7 inrermedium genes a9. a27. a62, a63, a12. a36, and a65. The only four-gene segregation included a9, c63. d12, and e65. Awn development, fertility, and seed development for lateral florets of the main spike showed a highly significant promotion in three-gene segregants compared with the corresponding double mutants. An apparent further progressive enhancement of the lateral floret charactera was obtained when a fourth intermedium gene was introduced into the segregation, particularly for fertility and seed size. This observation may have practically important implications for plant breeding in six-rowed barley, when specifically efficient constellations of alleles belonging to different intermedium loci have been tried out.

The interactive competence of a number of genes promoting lateral floret development in barley was studied with particular reference to the interaction in dihybrid and trihybrid F2 segregations after crossing involving the six-row locus hex-v and the three most frequently mutating recessive intermedium loci. int-a, int-c. and int-e. The former locus was represented by the mutation hex-v3 (derived from the two-row variety ‘Bonus’) and the allelic state hex-vA in the six-row commercial variety ‘Agneta’. The latter loci were each represented by three allcles (-a9, -a10 -a27; -c5 -c13 -c29; -e20-e23 -e65) derived from the two-row varieties ‘Bonus’ or ‘Foma’, whereas ‘Agneta’ contributed the int-c allele -cA. F2 data for lateral floret characters (awn length. fertility, seed size) were contrasted to standards considered to provide the phenotypic spectra corresponding to the different genotypic constituents of the F2 segregations. The analyses of observed data in relation to expectations on various hypotheses for interaction between hex-v and the recessive int genes led to the following main conclusions. In no case were there indications of total failure to enhance the phenotypic expression above the level of the corresponding standard categories. The degrees of phenotypic enhancement may differ among characters of lateral floret development, among int loci, and among allelic states of the latter, whereas differences between the two representatives of hex-v were not discernible.

The interactive competence of the genes promoting lateral floret development in the successful Svalof six-row variety ‘Agneta’ was studied. In this variety, genes for enhanced development of lateral florets occur not only at the six-row locus hex-v, but also at a recessive intermedium locus, int-c. Three int-c mutants, c5, c13, and c29, were crossed to ‘Agneta thus there was no dominant normal allele at int-c present in the crosses, whereas the hex-v locus would segregate for the normal and the six-row allelic states. F2 data for lateral floret characters (awn length, fertility, seed size) were contrasted to standards considered to provide the phenotypic spectra corresponding to the different genotypic constituents of the F2 segregations (two-row variety, VV CC; int-c mutants, Wcc; six-row mutant, vv CC; and six-rowed variety ‘Agneta’, vv cc). The analyses of observed data in relation to expectations on various hypotheses for interaction between hex-v and int-c led to the following main conclusions. The degrees of phenotypic enhancement may differ among characters of lateral floret development and among int-c mutant genes. There are no indications that the int-c allele present in ‘Agneta’ is the superior enhancer of the hex-v gene vA in this variety. Nor can we presume that vA is a superior six-row gene. Most probably, it would pay the efforts in a plant-breeding program with six-row barley to try various constellations of hex-v and int-c mutants.

A sodium azide-mutagenized population of barley (cv. 'Morex') was developed and utilized to identify mutants at target genes using the 'targeting induced local lesions in genomes' (TILLING) procedure. Screening for mutations at four agronomically important genes (HvCO1, Rpg1, eIF4E and NR) identified a total of 22 new mutant alleles, equivalent to the extrapolated rate of one mutation every 374 kb. All mutations except one were G/C to A/T transitions and several (approximately 68%) implied a change in protein amino acid sequence and therefore a possible effect on phenotype. The high rate of mutation detected through TILLING is in keeping with the high frequency (32.7%) of variant phenotypes observed amongst the M(3) families. Our results indicate the feasibility of using this resource for both reverse and forward genetics approaches to investigate gene function in barley and related crops.

Among 103 intermedium mutants induced in two-row cultivated barleys, and localized to 11 int loci, 5 of which being represented by one mutant each, no definite preference to the type of mutagen applied was found. There are clear morphological distinctions among intermedium mutants belonging to different loci, but also among allelic mutants; and there is an obvious distinction between intermedium mutants and the mutants belonging to the locus hex-v. Among the int mutants, only the int-d alleles show dominance, which is variable among the 13 alleles studied and also for the individual d allele. F2 data from crosses among int mutants showed no undisputable linkage among the 9 int loci studied in their normal positions. In spite of factors disturbing this analysis, mainly phenotypic overlapping and the variable dominance characterizing locus int-d, the 9 loci int-a, -b, -c, -d, -e, -f -h, -i, and int-k may for practical purposes be considered to approach an independent inheritance in relation to one another.

After treatments with ionizing radiations and chemicals in the commercial barley varieties ‘Bonus’, ‘Mari’, ‘Pallas;’, and ‘Kristina’, 43 lines with dominant resistance to the mildew race D1 were isolated, 34 in infection tests on M3 seedlings from M2 spikes, and 9 as resistant M2 seedlings from M1 spikes. Genetical analyses of these dominant resistant lines included crosses to susceptible material, crosses to the ml-o variety ‘Reforma’, crosses among the lines, crosses to sources of known dominant resistance genes, and tests to a panel of 30 different races of barley powdery mildew. In the panel tests, 27 among the lines showed resistance spectra similar or identical to Ml-a7, Ml-a9, Ml-a12, Ml-a13, Ml-a3 + Tu2 in Sv 57/510-44, Ml-g, and Ml- (La), whereas the remaining 16 lines formed 12 groups showing new spectra of resistance. The genetical analyses of F2 and F3 data from crosses indicate that the majority of the 43 lines are due to a restricted chromosomal segment in or close to the Ml-a region. There is ample evidence that the vast majority of the isolated dominant lines represent genuine mutations. Mutation breeding is suggested to offer a convenient way to introduce into the genome a tightly linked new dominant resistance gene, and so to create complex building-stones for further use in conventional combination breeding.

Lundovist, U. and Lundovist, A. 1987. An intermedium gene present in a commercial six-row variety of barley. —Hereditas 107 131–135. Lund. Sweden. ISSN 0018–0661. Received December 11, 1986 In a study of the inheritance of seven recessive intermedium loci (int-a, -b, -c, -e, -f -h, and -i) in relation to the semidominant six-row locus hex-v as contributed by the highbred commercial six-row variety Svalof s ‘Agneta’, F2 segregations unexpectedly revealed the presence, in this variety, of genes for enhanced development of lateral florets not only at the hex-v locus, but also at an intermedium locus, int-c. Further analyses demonstrated, among 18 alleles of int-c, a variable competence of conferring a six-row phenotype to cc Vv plants, with a single hex-v allele from ‘Agneta’. The int-c allele from ‘Agneta’ is not among the “strong” alleles. Nevertheless, this allele is likely to influence the phenotype of ‘Agneta’ favourably, in view of the fact that among mutants from the two-row state, at the hex-v locus, the development of lateral florets is generally variable, and that, in comparison with commercial six-row varieties, their lateral kernels are smaller, with shorter awns. An unintentional selection for enhancing int genes occurring as spontaneous mutations seems likely in commercial six-row varieties. Then, an optimal gene co-operation may have been attained in the ‘Agneta’ variety, “stronger”c alleles running the risk of going beyond this optimum. Or, we are just in the beginning of a deliberate use of the possibilities inherent in the co-operation between int genes and alleles at the hex-v locus.

The paper presents 1580 mutants affecting the deposition of epicuticular waxes in cultivated barley and localized to 79 different cer loci. These mutations have been induced by various mutagens: ionizing radiations, organic chemicals, and the inorganic sodium azide (NaN,). With special emphasis on mutations obtained after treatment with NaN3, the paper aims at a comprehensive analysis of mutagen specific reactions of cer loci. Different cer loci have different mutabilities, irrespectively of treatment with one or another mutagen, It is equally obvious that different cer loci quite frequently show markedly differing mutagen specific reactions. Whereas ethylene imine and sulfonates show similar patterns of mutagenic efficiency on the present cer loci, there are strong differences between the organic chemicals and sodium azide, which in its turn differs less from the physical mutagens X-rays and neutrons than do the organic chemicals. The relationships among the three main kinds of mutagen seem to be best visualized in the shape of a triangle than as points on a straight line.

A search for practically valuable mutant genes conferring resistance to barley powdery mildew applied a screening system where four commercial varieties of barley without known genes for resistance were tested to the successful mildew race D1. Ionizing radiations and chemicals were used as mutagens. Among the 71 resistant lines isolated, 28 were recessive and belonging to locus ml-o, and 43 were dominant. In tests to a panel of 30 different races of barley powdery mildew, 27 among the dominant lines showed resistance spectra similar or identical to those characterizing 7 previously known genes. The remaining 16 lines formed 12 groups displaying new spectra of resistance to the panel of mildew races. Taking the frequency of recessive mutations in locus ml-o as a standard, ionizing radiations were significantly more efficient mutagens for producing dominant resistance to mildew. In spite of some possible sources of contaminant dominant resistance genes, the evidence points at a vast majority of the isolated lines representing genuine dominant mutations. Being produced in a single mutational step, such dominant genes for resistance offer evidence of having a regulatory function, regulating aspects of the host metabolism of importance for or interfering with the pathogen development.

Classification des dihybrides F2 pour la deviation des taux attendus dans les combinaisons de gene en absence de linkage etudie par croisement entre 56 mutants intermedium appartenant a 8 loci int

We have previously described the evaluation of a cDNA microarray platform to identify and clone mutated barley (Hordeum vulgare L.) genes, using their transcriptionally defective mutant alleles (S. Zakhrabekova, C.G. Karmangara, D. von Wettstein, M. Hansson, A microarray approach for identification of mutated genes, Plant Physiol. Biochem. 40 (2002) 189-197). It was concluded that competitive hybridization between phenotypically similar mutants could specifically highlight an arrayed clone, corresponding to the mutated gene. In this study we evaluate whether the Affymetrix microarray platform can be used for the same purpose. The Affymetrix barley microarray contains a large number of clones (22,792 probe sets). In this and the previous study we used two barley mutant strains, xantha-h.57 and xantha-f.27, with known mutations in different subunit genes of the chlorophyll biosynthetic enzyme magnesium chelatase (EC 6.6. 1. 1). Mutant xantha-h.57 produces no Xantha-h mRNA whereas in xantha-f27 the nonsense mutation in the last exon of the gene, results in nonsense-mediated decay of Xantha-f mRNA. We conclude that the Affyinetrix platform meets our requirements and that our approach successfully highlighted the arrayed Xantha-h clone and that Xantha-f was among the top fourteen candidates.

Inflorescences of the tribe Triticeae, which includes wheat (Triticum sp. L.) and barley (Hordeum vulgare L.) are characterized by sessile spikelets directly borne on the main axis, thus forming a branchless spike. "Compositum-Barley" and tetraploid "Miracle-Wheat" (T. turgidum convar. compositum (L.f.) Filat.) display non-canonical spike-branching in which spikelets are replaced by lateral branch-like structures resembling small-sized secondary spikes. As a result of this branch formation "Miracle-Wheat" produces significantly more grains per spike, leading to higher spike yield. In this study, we first isolated the gene underlying spike-branching in "Compositum-Barley", i.e. compositum 2 (com2). Moreover, we found that COM2 is orthologous to the branched head(t) (bh(t)) locus regulating spike-branching in tetraploid "Miracle-Wheat". Both genes possess orthologs with similar functions in maize BRANCHED SILKLESS 1 (BD1) and rice FRIZZY PANICLE/BRANCHED FLORETLESS 1 (FZP/BFL1) encoding AP2/ERF transcription factors. Sequence analysis of the bh(t) locus in a collection of mutant and wild type tetraploid wheat accessions revealed that a single amino acid substitution in the DNA-binding domain gave rise to the domestication of "Miracle-Wheat". mRNA in situ hybridization, microarray experiments, and independent qRT-PCR validation analyses revealed that the branch repression pathway in barley is governed through the spike architecture gene Six-rowed spike 4 regulating COM2 expression, while HvIDS1 (barley ortholog of maize INDETERMINATE SPIKELET 1) is a putative down-stream target of COM2. These findings presented here provide new insights into the genetic basis of spike architecture in Triticeae, and have disclosed new targets for genetic manipulations aiming at boosting wheat's yield potential.

During the last 30 years, a collection of morphological barley mutants has been developed in Fiorenzuola d’Arda, Italy, as part of the international effort directed to the conservation of genetic stocks, to ensure the global availability and the correct maintenance of these genetic materials. The collection is comprehensive of stem, leaf, ear, flower, awn and grain mutants. Near isogenic lines (NILs) useful for genetic analysis and to study the effect of mutation on agronomic performance have been developed. New different hooded mutants have been obtained in rare outcrosses of the flower in the hood. The development of double and triple mutants obtained by intercrossing simple mutants has been done and will continue. The collection is continuously implemented by including new mutants through a collaborative work with the other germplasm banks and represents a unique source of alleles for better understanding the role of genes involved in plant architecture.

The barley (Hordeum vulgare L.) mutants fch2 and clo-f2 comprise an allelic group of 14 Chl b-deficient lines. The genetic map position of fch2 corresponds to the physical map position of the gene encoding chlorophyllide a oxygenase. This enzyme converts chlorophyllide a to chlorophyllide b and it is essential for Chl b biosynthesis. The fch2 and clo-f2 barley lines were shown to be mutated in the gene for chlorophyllide a oxygenase. A five-base insertion was found in fch2 and base deletions in clo-f2.101, clo-f2.105, clo-f2.2800 and clo-f2.3613. In clo-f2.105 and clo-f2.108, nonsense base exchanges were discovered. All of these mutations led to a premature stop of translation and none of the mutants formed Chl b. The mutant clo-f2.2807 was transcript deficient and formed no Chl b. Missense mutations in clo-f2.102 (leading to the amino acid exchange D495N) and clo-f2.103 (G280D) resulted in a total lack of Chl b, whereas in the missense mutants clo-f2.107 (P419L), clo-f2.109 (A94T), clo-f2.122 (C320Y), clo-f2.123 (A94T), clo-f2.133 (A376V) and clo-f2.181 (L373F) intermediate contents of Chl b were determined. The missense mutations affect conserved residues, and their effect on chlorophyllide a oxygenase is discussed. The mutations in clo-f2.102, clo-f2.103, clo-f2.133 and clo-f2.181 may influence electron transfer as illustrated in the active site of a structural model protein. The changes in clo-f2.107, clo-f2.109, clo-f2.122 and clo-f2.123 may lead to Chlb deficiency by interfering with the regulation of chlorophyllide a oxygenase. The correlation of mutations and phenotypes strongly supports that the barley locus fch2 encodes chlorophyllide a oxygenase.

The domestication of cereals has involved common changes in morphological features, such as seed size, seed retention and modification of vegetative and inflorescence architecture that ultimately contributed to an increase in harvested yield. In barley, this process has resulted in two different cultivated types, two-rowed and six-rowed forms, both derived from the wild two-rowed ancestor, with archaeo-botanical evidence indicating the origin of six-rowed barley early in the domestication of the species, some 8,600-8,000 years ago. Variation at SIX-ROWED SPIKE 1 (VRS1) is sufficient to control this phenotype. However, phenotypes imposed by VRS1 alleles are modified by alleles at the INTERMEDIUM-C (INT-C) locus. Here we show that INT-C is an ortholog of the maize domestication gene TEOSINTE BRANCHED 1 (TB1) and identify 17 coding mutations in barley TB1 correlated with lateral spikelet fertility phenotypes.

Background The economic importance of cereals such as barley, and the demand for improved yield and quality require a better understanding of the genetic components that modulate biologically and commercially relevant traits. While Arabidopsis thaliana is the premiere model plant system, the spectrum of its traits cannot address all of the fundamental questions of crop plant development. Unlike Arabidopsis, barley is both a crop and a model system for scientific research, and it is increasingly being used for genetic and molecular investigations into the conserved biological processes of cereals. A common challenge in genetic studies in plants with large genomes arises from the very time-consuming work of associating mutant phenotypes with gene sequence information, especially if insertion mutagenesis is not routine, as in barley. Reverse genetics based on chemical mutagenesis represents the best solution to this obstacle. Findings In barley, we generated a new TILLING (Targeting Local Lesions IN Genomes) resource comprising 10,279 M2 mutants in the two-rowed malting cultivar 'Barke,' which has been used in the generation of other genomic resources in barley (~150,000 ESTs, DH mapping population). The value of this new resource was tested using selected candidate genes. An average frequency of approximately one mutation per 0.5 Mb was determined by screening ten fragments of six different genes. The ethyl methanesulphonate (EMS)mutagenesis efficiency was studied by recording and relating the mutagenesis-dependent effects found in the three mutant generations (M1-M3). A detailed analysis was performed for the homeodomain-leucine-zipper (HD-ZIP) gene HvHox1. Thirty-one mutations were identified by screening a 1,270-bp fragment in 7,348 M2 lines. Three of the newly identified mutants exhibited either a six-rowed or an intermedium-spike phenotype, and one mutant displayed a significantly altered spikelet morphology compared to that of the 'Barke' wild type. Our results indicate a bias in the frequency of independent functional mutations at specific base pair (bp) positions within the gene HvHox1. Conclusions A new TILLING population was developed as a resource for high-throughput gene discovery in an alternative barley germplasm. Pilot screening demonstrated a similar or even slightly higher mutation frequency when compared to previously published barley TILLING populations that should allow for the identification of diverse allelic variation. Partial phenotypic evaluation of the M2 and M3 generations has revealed the presence of a wide spectrum of morphological diversity that highlights the great potential of this resource for use in forward genetic screens. Altogether, our study shows the efficiency of screening and the applicability of the new TILLING population for genetic studies in the barley crop model system.

Increased seed production has been a common goal during the domestication of cereal crops, and early cultivators of barley ( Hordeum vulgare ssp. vulgare ) selected a phenotype with a six-rowed spike that stably produced three times the usual grain number. This improved yield established barley as a founder crop for the Near Eastern Neolithic civilization. The barley spike has one central and two lateral spikelets at each rachis node. The wild-type progenitor ( H. vulgare ssp. spontaneum ) has a two-rowed phenotype, with additional, strictly rudimentary, lateral rows; this natural adaptation is advantageous for seed dispersal after shattering. Until recently, the origin of the six-rowed phenotype remained unknown. In the present study, we isolated vrs1 ( six-rowed spike 1 ), the gene responsible for the six-rowed spike in barley, by means of positional cloning. The wild-type Vrs1 allele (for two-rowed barley) encodes a transcription factor that includes a homeodomain with a closely linked leucine zipper motif. Expression of Vrs1 was strictly localized in the lateral-spikelet primordia of immature spikes, suggesting that the VRS1 protein suppresses development of the lateral rows. Loss of function of Vrs1 resulted in complete conversion of the rudimentary lateral spikelets in two-rowed barley into fully developed fertile spikelets in the six-rowed phenotype. Phylogenetic analysis demonstrated that the six-rowed phenotype originated repeatedly, at different times and in different regions, through independent mutations of Vrs1 .