The Importance of Barley Genetics and Domestication in a Global Perspective

Background Archaeological evidence has revealed that barley (Hordeum vulgare) is one of the oldest crops used by ancient farmers. Studies of the time and place of barley domestication may help in understanding ancient human civilization. Scope The studies of domesticated genes in crops have uncovered the mechanisms which converted wild and unpromising wild species to the most important food for humans. In addition to archaeological studies, molecular studies are finding new insights into the process of domestication. Throughout the process of barley domestication human selection on wild species resulted in plants with more harvestable seeds. One of the remarkable changes during barley domestications was the appearance of six-rowed barley. The gene associated with this trait results in three times more seed per spike compared with ancestral wild barley. This increase in number of seed resulted in a major dichotomy in the evolution of barley. The identification of the six-rowed spike gene provided a framework for understanding how this character was evolved. Some important barley domestication genes have been discovered and many are currently being investigated. Conclusions Identification of domestication genes in crops revealed that most of the drastic changes during domestication are the result of functional impairments in transcription factor genes, and creation of new functions is rare. Isolation of the six-rowed spike gene revealed that this trait was domesticated more than once in the domestication history of barley. Six-rowed barley is derived from two-rowed ancestral forms. Isolation of photoperiod-response genes in barley and rice revealed that different genes belonging to similar genetic networks partially control this trait

TILLING in the two-rowed barley cultivar 'Barke' reveals preferred sites of functional diversity in the gene HvHox1

<p>Abstract</p> <p>Background</p> <p>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 <it>Arabidopsis thaliana </it>is the premiere model plant system, the spectrum of its traits cannot address all of the fundamental questions of crop plant development. Unlike <it>Arabidopsis</it>, 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.</p> <p>Findings</p> <p>In barley, we generated a new TILLING (Targeting Local Lesions IN Genomes) resource comprising 10,279 M₂mutants 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 <it>HvHox1</it>. Thirty-one mutations were identified by screening a 1,270-bp fragment in 7,348 M₂lines. Three of the newly identified mutants exhibited either a six-rowed or an <it>intermedium</it>-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 <it>HvHox1</it>.</p> <p>Conclusions</p> <p>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 M₂and M₃generations 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.</p

Mapping of QTL for intermedium spike on barley chromosome 4H using EST-based markers

The lateral spikelets of two-rowed barley are reduced in size and sterile, but in six-rowed barley all three spikelets are fully fertile. The trait is largely controlled by alleles at the vrs1 locus on chromosome arm 2HL, as modified by the allele present at the I locus on chromosome arm 4HS. Molecular markers were developed to saturate the 4HS region by exploiting expressed sequence-tags, either previously mapped in barley to this region, or present in the syntenic region of rice chromosome 3. Collinearity between rice and barley was strong in the 4.8 cM interval BJ468164-AV933435 and the 10 cM interval AV942364-BJ455560. A major QTL for lateral spikelet fertility (the I locus) explained 44% of phenotypic variance, and was located in the interval CB873567-BJ473916. The genotyping of near-isogenic lines for I placed the locus in a region between CB873567 and EBmac635, and therefore the most likely position of the I locus was proximal to CB873567 in a 5.3 cM interval between CB873567-BJ473916

Mapping of the eibi1 gene responsible for the drought hypersensitive cuticle in wild barley (Hordeum spontaneum)

Segregation analysis showed that eibi1, a drought hypersensitive Cuticle wild barley mutant, was monogenic and recessive, and mapped in two F, Populations, one made from a cross between the mutant and a Cultivated barley (cv. Morex), and the other between the mutant and another wild barley. A microsatellite marker screen showed that the gene was located oil barley chromosome 3H, and a set of markers already assigned to this chromosome, including both microsatellites and ESTs, was used to construct a genetic map. eibi1 co-segregated with barley EST AV918546, and was located to bin 6. The synteny between barley and rice ill this region is incomplete, with a large discrepancy in map distances, and the presence Of Multiple inversions

A new Vrs1 allele identified in 2-row Spanish landraces

1 .pdf copy (A3) of the original poster presented by the Authors.Vrs1, the gene determining the type of spike in barley has been extensively studied. The wild dominant allele encodes a homeodomain-leucine zipper transcription factor whose activity results in a two-rowed spike, whereas the recessive allele produces a six-row phenotype. Phylogenetic analysis of barley cultivars identified two alleles in two-rowed types and at least four different alleles in six-rowed barleys. Previous results genotyping with MWG699, a marker closely linked to Vrs1, suggested different geographic origins for six-row alleles, among them the vrs1.a2 allele originated in the Western Mediterranean. Using this same marker, we showed that a large proportion of Spanish and Moroccan landraces (both 2- and 6-rowed) as well as Moroccan Hordeum spontaneum lines, all shared the same haplotype. We then analyzed the sequence of the Vrs1 gene in those lines. All (11) six-rowed barleys sequenced carried the vrs1.a2 allele, but we found different Vrs1 alleles among 2-rowed types: the material from Morocco, both wild (3) and cultivated (2), carried the Vrs1.b2 allele, which was absent from the Spanish 2-rowed landraces studied. The most common allele among these was Vrs1.b3, in 46 lines out of 53 evaluated. The other seven lines presented a new Vrs1 allele, Vrs1.b5. This new allele contains a ‘T’ insertion in exon 2, originally proposed as the causal mutation giving rise to the 6-row vrs1.a2 allele, but has an additional upstream deletion that results in the change of 15 amino acids and a potentially functional protein. These results add a new hypothesis to the origin of the 6-rowed vrs1.a2 allele, which could result from a mutation either at the Vrs1.b2 allele (classical hypothesis) or at the newly found Vrs1.b5 allele identified in Spanish landraces.Peer reviewe

Resequencing the Vrs1 gene in Spanish barley landraces revealed reversion of six-rowed to two-rowed spike

Six-rowed spike 1 (Vrs1) is a gene of major importance for barley breeding and germplasm management as it is the main gene determining spike row-type (2-rowed vs. 6-rowed). This is a widely used DUS trait, and has been often associated to phenotypic traits beyond spike type. Comprehensive re-sequencing Vrs1 revealed three two-rowed alleles (Vrs1.b2; Vrs1.b3; Vrs1.t1) and four six-rowed (vrs1.a1; vrs1.a2; vrs1.a3; vrs1.a4) in the natural population. However, the current knowledge about Vrs1 alleles and its distribution among Spanish barley subpopulations is still underexploited. We analyzed the gene in a panel of 215 genotypes, made of Spanish landraces and European cultivars. Among 143 six-rowed accessions, 57 had the vrs1.a1 allele, 83 were vrs1.a2, and three showed the vrs1.a3 allele. Vrs1.b3 was found in most two-rowed accessions, and a new allele was observed in 7 out of 50 two-rowed Spanish landraces. This allele, named Vrs1.b5, contains a ‘T’ insertion in exon 2, originally proposed as the causal mutation giving rise to the six-row vrs1.a2 allele, but has an additional upstream deletion that results in the change of 15 amino acids and a potentially functional protein. We conclude that eight Vrs1 alleles (Vrs1.b2, Vrs1.b3, Vrs1.b5, Vrs1.t1, vrs1.a1, vrs1.a2, vrs1.a3, vrs1.a4) discriminate two and six-rowed barleys. The markers described will be useful for DUS identification, plant breeders, and other crop scientists.This work was supported by the Spanish Ministry of Economy, Industry and Competitiveness grants AGL2010-21929, AGL2013-48756-R, RFP2012-00015-00-00, RTA2012-00033-C03-02, and EUI2009-04075 (national code for Plant-KBBE project ExpResBar). CPC was funded by the Spanish Ministry of Economy, Industry and Competitiveness grant no. BES-2011-045905 (linked to project AGL2010-21929). TK and SS were supported by a research fund by the Ministry of Agriculture, Forestry, and Fisheries of Japan (Genomics for Agricultural Innovation grants no. TRS1002). SS was supported by a Grant-in-Aid from the Japan Society for the Promotion of Science (JSPS) Postdoctoral Fellow for Research Abroad and a Grant-in-Aid for Young Scientists (B) (no. 16 K18635)

Extreme Suppression of Lateral Floret Development by a Single Amino Acid Change in the VRS1 Transcription Factor

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

Unleashing floret fertility in wheat through the mutation of a homeobox gene

Floret fertility is a key determinant of the number of grains per inflorescence in cereals. During the evolution of wheat (Triticum sp.), floret fertility has increased, such that current bread wheat (Triticum aestivum) cultivars set three to five grains per spikelet. However, little is known regarding the genetic basis of floret fertility. The locus Grain Number Increase 1 (GNI1) is shown here to be an important contributor to floret fertility. GNI1 evolved in the Triticeae through gene duplication. The gene, which encodes a homeodomain leucine zipper class I (HD-Zip I) transcription factor, was expressed most abundantly in the most apical floret primordia and in parts of the rachilla, suggesting that it acts to inhibit rachilla growth and development. The level of GNI1 expression has decreased over the course of wheat evolution under domestication, leading to the production of spikes bearing more fertile florets and setting more grains per spikelet. Genetic analysis has revealed that the reduced-function allele GNI-A1 contributes to the increased number of fertile florets per spikelet. The RNAi-based knockdown of GNI1 led to an increase in the number of both fertile florets and grains in hexaploid wheat. Mutants carrying an impaired GNI-A1 allele out-yielded WT allele carriers under field conditions. The data show that gene duplication generated evolutionary novelty affecting floret fertility while mutations favoring increased grain production have been under selection during wheat evolution under domestication