early maturity 7 promotes early flowering by controlling the light input into the circadian clock in barley.

Breeding for variation in photoperiod response is crucial to adapt crop plants to various environments. Plants measure changes in day length by the circadian clock, an endogenous timekeeper that allows plants to anticipate changes in diurnal and seasonal light-dark cycles. Here, we describe the early maturity 7 (eam7) locus in barley (Hordeum vulgare), which interacts with PHOTOPERIOD 1 (Ppd-H1) to cause early flowering under non-inductive short days. We identify LIGHT-REGULATED WD 1 (LWD1) as a putative candidate to underlie the eam7 locus in barley as supported by genetic mapping and CRISPR-Cas9-generated lwd1 mutants. Mutations in eam7 cause a significant phase advance and a misregulation of core clock and clock output genes under diurnal conditions. Early flowering was linked to an upregulation of Ppd-H1 during the night and consequent induction of the florigen FLOWERING LOCUS T1 under short days. We propose that EAM7 controls photoperiodic flowering in barley by controlling the light input into the clock and diurnal expression patterns of the major photoperiod response gene Ppd-H1.

WAPO-A1 is the causal gene of the 7AL QTL for spikelet number per spike in wheat.

Improving our understanding of the genes regulating grain yield can contribute to the development of more productive wheat varieties. Previously, a highly significant QTL affecting spikelet number per spike (SNS), grain number per spike (GNS) and grain yield was detected on chromosome arm 7AL in multiple genome-wide association studies. Using a high-resolution genetic map, we established that the A-genome homeolog of WHEAT ORTHOLOG OF APO1 (WAPO-A1) was a leading candidate gene for this QTL. Using mutants and transgenic plants, we demonstrate in this study that WAPO-A1 is the causal gene underpinning this QTL. Loss-of-function mutants wapo-A1 and wapo-B1 showed reduced SNS in tetraploid wheat, and the effect was exacerbated in wapo1 combining both mutations. By contrast, spikes of transgenic wheat plants carrying extra copies of WAPO-A1 driven by its native promoter had higher SNS, a more compact spike apical region and a smaller terminal spikelet than the wild type. Taken together, these results indicate that WAPO1 affects SNS by regulating the timing of terminal spikelet formation. Both transgenic and wapo1 mutant plants showed a wide range of floral abnormalities, indicating additional roles of WAPO1 on wheat floral development. Previously, we found three widespread haplotypes in the QTL region (H1, H2 and H3), each associated with particular WAPO-A1 alleles. Results from this and our previous study show that the WAPO-A1 allele in the H1 haplotype (115-bp deletion in the promoter) is expressed at significantly lower levels in the developing spikes than the alleles in the H2 and H3 haplotypes, resulting in reduced SNS. Field experiments also showed that the H2 haplotype is associated with the strongest effects in increasing SNS and GNS (H2>H3>H1). The H2 haplotype is already present in most modern common wheat varieties but is rare in durum wheat, where it might be particularly useful to improve grain yield.

INTERMEDIUM-M encodes an HvAP2L-H5 ortholog and is required for inflorescence indeterminacy and spikelet determinacy in barley.

Inflorescence architecture dictates the number of flowers and, ultimately, seeds. The architectural discrepancies between two related cereals, barley and wheat, are controlled by differences in determinacy of inflorescence and spikelet meristems. Here, we characterize two allelic series of mutations named intermedium-m (int-m) and double seed1 (dub1) that convert barley indeterminate inflorescences into wheat-like determinate inflorescences bearing a multifloreted terminal spikelet and spikelets with additional florets. INT-M/DUB1 encodes an APETALA2-like transcription factor (HvAP2L-H5) that suppresses ectopic and precocious spikelet initiation signals and maintains meristem activity. HvAP2L-H5 inhibits the identity shift of an inflorescence meristem (IM) to a terminal spikelet meristem (TSM) in barley. Null mutations in AP2L-5 lead to fewer spikelets per inflorescence but extra florets per spikelet. In wheat, prolonged and elevated AP2L-A5 activity in rAP2L-A5 mutants delays but does not suppress the IM-TSM transition. We hypothesize that the regulation of AP2L-5 orthologs and downstream genes contributes to the different inflorescence determinacy in barley and wheat. We show that AP2L-5 proteins are evolutionarily conserved in grasses, promote IM activity, and restrict floret number per spikelet. This study provides insights into the regulation of spikelet and floret number, and hence grain yield in barley and wheat.

An Acyl-CoA N-Acyltransferase Regulates Meristem Phase Change and Plant Architecture in Barley.

The modification of shoot architecture and increased investment into reproductive structures is key for crop improvement and is achieved through coordinated changes in the development and determinacy of different shoot meristems. A fundamental question is how the development of different shoot meristems is genetically coordinated to optimize the balance between vegetative and reproductive organs. Here we identify the MANY NODED DWARF1 (HvMND1) gene as a major regulator of plant architecture in barley (Hordeum vulgare). The mnd1.a mutant displayed an extended vegetative program with increased phytomer, leaf, and tiller production but a reduction in the number and size of grains. The induction of vegetative structures continued even after the transition to reproductive growth, resulting in a marked increase in longevity. Using mapping by RNA sequencing, we found that the HvMND1 gene encodes an acyl-CoA N-acyltransferase that is predominately expressed in developing axillary meristems and young inflorescences. Exploration of the expression network modulated by HvMND1 revealed differential expression of the developmental microRNAs miR156 and miR172 and several key cell cycle and developmental genes. Our data suggest that HvMND1 plays a significant role in the coordinated regulation of reproductive phase transitions, thereby promoting reproductive growth and whole plant senescence in barley.

Differential Effects of Day/Night Cues and the Circadian Clock on the Barley Transcriptome.

The circadian clock is a complex transcriptional network that regulates gene expression in anticipation of the day/night cycle and controls agronomic traits in plants. However, in crops, how the internal clock and day/night cues affect the transcriptome remains poorly understood. We analyzed the diel and circadian leaf transcriptomes in the barley (Hordeum vulgare) cultivar 'Bowman' and derived introgression lines harboring mutations in EARLY FLOWERING3 (ELF3), LUX ARRHYTHMO1 (LUX1), and EARLY MATURITY7 (EAM7). The elf3 and lux1 mutants exhibited abolished circadian transcriptome oscillations under constant conditions, whereas eam7 maintained oscillations of ≈30% of the circadian transcriptome. However, day/night cues fully restored transcript oscillations in all three mutants and thus compensated for a disrupted oscillator in the arrhythmic barley clock mutants elf3 and lux1 Nevertheless, elf3, but not lux1, affected the phase of the diel oscillating transcriptome and thus the integration of external cues into the clock. Using dynamical modeling, we predicted a structure of the barley circadian oscillator and interactions of its individual components with day/night cues. Our findings provide a valuable resource for exploring the function and output targets of the circadian clock and for further investigations into the diel and circadian control of the barley transcriptome.

Ppd-H1 integrates drought stress signals to control spike development and flowering time in barley.

Drought impairs growth and spike development, and is therefore a major cause of yield losses in the temperate cereals barley and wheat. Here, we show that the photoperiod response gene PHOTOPERIOD-H1 (Ppd-H1) interacts with drought stress signals to modulate spike development. We tested the effects of a continuous mild and a transient severe drought stress on developmental timing and spike development in spring barley cultivars with a natural mutation in ppd-H1 and derived introgression lines carrying the wild-type Ppd-H1 allele from wild barley. Mild drought reduced the spikelet number and delayed floral development in spring cultivars but not in the introgression lines with a wild-type Ppd-H1 allele. Similarly, drought-triggered reductions in plant height, and tiller and spike number were more pronounced in the parental lines compared with the introgression lines. Transient severe stress halted growth and floral development; upon rewatering, introgression lines, but not the spring cultivars, accelerated development so that control and stressed plants flowered almost simultaneously. These genetic differences in development were correlated with a differential down-regulation of the flowering promotors FLOWERING LOCUS T1 and the BARLEY MADS-box genes BM3 and BM8. Our findings therefore demonstrate that Ppd-H1 affects developmental plasticity in response to drought in barley.

FLOWERING LOCUS T4 delays flowering and decreases floret fertility in barley.

FLOWERING LOCUS T-like (FT-like) genes control the photoperiodic regulation of flowering in many angiosperm plants. The family of FT-like genes is characterized by extensive gene duplication and subsequent diversification of FT functions which occurred independently in modern angiosperm lineages. In barley, there are 12 known FT-like genes (HvFT), but the function of most of them remains uncharacterized. This study aimed to characterize the role of HvFT4 in flowering time control and development in barley. The overexpression of HvFT4 in the spring cultivar Golden Promise delayed flowering time under long-day conditions. Microscopic dissection of the shoot apical meristem revealed that overexpression of HvFT4 specifically delayed spikelet initiation and reduced the number of spikelet primordia and grains per spike. Furthermore, ectopic overexpression of HvFT4 was associated with floret abortion and with the down-regulation of the barley MADS-box genes VRN-H1, HvBM3, and HvBM8 which promote floral development. This suggests that HvFT4 functions as a repressor of reproductive development in barley. Unraveling the genetic basis of FT-like genes can contribute to the identification of novel breeding targets to modify reproductive development and thereby spike morphology and grain yield.

CENTRORADIALIS Interacts with FLOWERING LOCUS T-Like Genes to Control Floret Development and Grain Number.

CENTRORADIALIS (CEN) is a key regulator of flowering time and inflorescence architecture in plants. Natural variation in the barley (Hordeum vulgare) homolog HvCEN is important for agricultural range expansion of barley cultivation, but its effects on shoot and spike architecture and consequently yield have not yet been characterized. Here, we evaluated 23 independent hvcen, also termed mat-c, mutants to determine the pleiotropic effects of HvCEN on developmental timing and shoot and spike morphologies of barley under outdoor and controlled conditions. All hvcen mutants flowered early and showed a reduction in spikelet number per spike, tiller number, and yield in the outdoor experiments. Mutations in hvcen accelerated spikelet initiation and reduced axillary bud number in a photoperiod-independent manner but promoted floret development only under long days (LDs). The analysis of a flowering locus t3 (hvft3) hvcen double mutant showed that HvCEN interacts with HvFT3 to control spikelet initiation. Furthermore, early flowering3 (hvelf3) hvcen double mutants with high HvFT1 expression levels under short days suggested that HvCEN interacts with HvFT1 to repress floral development. Global transcriptome profiling in developing shoot apices and inflorescences of mutant and wild-type plants revealed that HvCEN controlled transcripts involved in chromatin remodeling activities, cytokinin and cell cycle regulation and cellular respiration under LDs and short days, whereas HvCEN affected floral homeotic genes only under LDs. Understanding the stage and organ-specific functions of HvCEN and downstream molecular networks will allow the manipulation of different shoot and spike traits and thereby yield.

Subfamily-Specific Specialization of RGH1/MLA Immune Receptors in Wild Barley.

The barley disease resistance (R) gene locus mildew locus A (Mla) provides isolate-specific resistance against the powdery mildew fungus Blumeria graminis hordei and has been introgressed into modern cultivars from diverse germplasms, including the wild relative Hordeum spontaneum. Known Mla disease resistance specificities to B. graminis hordei appear to encode allelic variants of the R gene homolog 1 (RGH1) family of nucleotide-binding domain and leucine-rich repeat (NLR) proteins. Here, we sequenced and assembled the transcriptomes of 50 H. spontaneum accessions representing nine populations distributed throughout the Fertile Crescent. The assembled Mla transcripts exhibited rich sequence diversity, linked neither to geographic origin nor population structure, and could be grouped into two similar-sized subfamilies based on two major N-terminal coiled-coil (CC) signaling domains that are both capable of eliciting cell death. The presence of positively selected sites located mainly in the C-terminal leucine-rich repeats of both MLA subfamilies, together with the fact that both CC signaling domains mediate cell death, implies that the two subfamilies are actively maintained in the population. Unexpectedly, known MLA receptor variants that confer B. graminis hordei resistance belong exclusively to one subfamily. Thus, signaling domain divergence, potentially as adaptation to distinct pathogen populations, is an evolutionary signature of functional diversification of an immune receptor. Copyright © 2018 The Author(s). This is an open access article distributed under the CC BY-NC-ND 4.0 International license .

FLOWERING LOCUS T3 Controls Spikelet Initiation But Not Floral Development.

In many angiosperm plants, FLOWERING LOCUS T (FT)-like genes have duplicated and functionally diverged to control different reproductive traits or stages. Barley (Hordeum vulgare) carries several FT-like genes, the functions of which are not well understood. We characterized the role of HvFT3 in the vegetative and reproductive development of barley. Overexpression of HvFT3 accelerated the initiation of spikelet primordia and the early reproductive development of spring barley independently of the photoperiod. However, HvFT3 overexpression did not accelerate floral development, and inflorescences aborted under short days, suggesting that HvFT3 controls spikelet initiation but not floral development. Analysis of a nonfunctional HvFT3 allele supported the specific effects of this gene on spikelet initiation independent of the photoperiod. HvFT3 caused the up-regulation of the winter and spring alleles of the vernalization gene VERNALIZATION1 (VRN-H1) in nonvernalized plants and was therefore dominant over the repressive effects of the vernalization pathway. Global transcriptome analysis in developing main shoot apices of the transgenic lines showed that HvFT3 modified the expression of genes involved in hormone synthesis and response, of floral homeotic genes, and of barley row-type genes SIX-ROWED-SPIKE1 (VRS1), SIX-ROWED-SPIKE4 (VRS4), and INTERMEDIUM C Understanding the specific functions of individual FT-like genes will allow modification of individual phases of preanthesis development and thereby adaptation to different environments and improved yield.

Targeted resequencing reveals genomic signatures of barley domestication.

Barley (Hordeum vulgare) is an established model to study domestication of the Fertile Crescent cereals. Recent molecular data suggested that domesticated barley genomes consist of the ancestral blocks descending from multiple wild barley populations. However, the relationship between the mosaic ancestry patterns and the process of domestication itself remained unclear. To address this knowledge gap, we identified candidate domestication genes using selection scans based on targeted resequencing of 433 wild and domesticated barley accessions. We conducted phylogenetic, population structure, and ancestry analyses to investigate the origin of the domesticated barley haplotypes separately at the neutral and candidate domestication loci. We discovered multiple selective sweeps that occurred on all barley chromosomes during domestication in the background of several ancestral wild populations. The ancestry analyses demonstrated that, although the ancestral blocks of the domesticated barley genomes were descended from all over the Fertile Crescent, the candidate domestication loci originated specifically in its eastern and western parts. These findings provided the first molecular evidence implicating multiple wild or protodomesticated lineages in the process of barley domestication initiated in the Levantine and Zagros clusters of the origin of agriculture.

The Genetic Control of Reproductive Development under High Ambient Temperature.

Ambient temperature has a large impact on reproductive development and grain yield in temperate cereals. However, little is known about the genetic control of development under different ambient temperatures. Here, we demonstrate that in barley (Hordeum vulgare), high ambient temperatures accelerate or delay reproductive development depending on the photoperiod response gene PHOTOPERIOD1 (Ppd-H1) and its upstream regulator EARLY FLOWERING3 (HvELF3). A natural mutation in Ppd-H1 prevalent in spring barley delayed floral development and reduced the number of florets and seeds per spike, while the wild-type Ppd-H1 or a mutant Hvelf3 allele accelerated floral development and maintained the seed number under high ambient temperatures. High ambient temperature delayed the expression phase and reduced the amplitude of clock genes and repressed the floral integrator gene FLOWERING LOCUS T1 independently of the genotype. Ppd-H1-dependent variation in flowering time under different ambient temperatures correlated with relative expression levels of the BARLEY MADS-box genes VERNALIZATION1 (HvVRN1), HvBM3, and HvBM8 in the leaf. Finally, we show that Ppd-H1 interacts with regulatory variation at HvVRN1. Ppd-H1 only accelerated floral development in the background of a spring HvVRN1 allele with a deletion in the regulatory intron. The full-length winter Hvvrn1 allele was strongly down-regulated, and flowering was delayed by high temperatures irrespective of Ppd-H1 Our findings demonstrate that the photoperiodic and vernalization pathways interact to control flowering time and floret fertility in response to ambient temperature in barley.

Six-Rowed Spike3 (VRS3) Is a Histone Demethylase That Controls Lateral Spikelet Development in Barley.

The complex nature of crop genomes has long prohibited the efficient isolation of agronomically relevant genes. However, recent advances in next-generation sequencing technologies provide new ways to accelerate fine-mapping and gene isolation in crops. We used RNA sequencing of allelic six-rowed spike3 (vrs3) mutants with altered spikelet development for gene identification and functional analysis in barley (Hordeum vulgare). Variant calling in two allelic vrs3 mutants revealed that VRS3 encodes a putative histone Lys demethylase with a conserved zinc finger and Jumonji C and N domain. Sanger sequencing of this candidate gene in independent allelic vrs3 mutants revealed a series of mutations in conserved domains, thus confirming our candidate as the VRS3 gene and suggesting that the row type in barley is determined epigenetically. Global transcriptional profiling in developing shoot apical meristems of vrs3 suggested that VRS3 acts as a transcriptional activator of the row-type genes VRS1 (Hv.HOMEOBOX1) and INTERMEDIUM-C (INT-C; Hv.TEOSINTE BRANCHED1). Comparative transcriptome analysis of the row-type mutants vrs3, vrs4 (Hv.RAMOSA2), and int-c confirmed that all three genes act as transcriptional activators of VRS1 and quantitative variation in the expression levels of VRS1 in these mutants correlated with differences in the number of developed lateral spikelets. The identification of genes and pathways affecting seed number in small grain cereals will enable to further unravel the transcriptional networks controlling this important yield component.

Global Transcriptome Profiling of Developing Leaf and Shoot Apices Reveals Distinct Genetic and Environmental Control of Floral Transition and Inflorescence Development in Barley.

Timing of the floral transition and inflorescence development strongly affect yield in barley (Hordeum vulgare). Therefore, we examined the effects of daylength and the photoperiod response gene PHOTOPERIOD1 (Ppd-H1) on barley development and analyzed gene expression changes in the developing leaves and main shoot apices (MSAs) of barley by RNA sequencing. The daylength sensitivity of MSA development had two phases, floret primordia initiated under long and short days, whereas successful inflorescence development occurred only under long days. The transcripts associated with floral transition were largely regulated independently of photoperiod and allelic variation at Ppd-H1. The photoperiod- and Ppd-H1-dependent differences in inflorescence development and flower fertility were associated with the induction of barley FLOWERING LOCUS T orthologs: FT1 in leaves and FT2 in MSAs. FT1 expression was coregulated with transcripts involved in nutrient transport, carbohydrate metabolism, and cell cycle regulation, suggesting that FT1 might alter source-sink relationships. Successful inflorescence development correlated with upregulation of FT2 and transcripts related to floral organ development, phytohormones, and cell cycle regulation. Identification of photoperiod and stage-specific transcripts gives insights into the regulation of reproductive development in barley and provides a resource for investigation of the complexities of development and yield in temperate grasses.

CONSTANS Controls Floral Repression by Up-Regulating VERNALIZATION2 (VRN-H2) in Barley.

In barley (Hordeum vulgare), PHOTOPERIOD1 (Ppd-H1) acts as a major positive regulator of flowering under long-day conditions, while VERNALIZATION2 (VRN-H2) is a strong repressor of flowering under long days before vernalization. By contrast, CONSTANS (CO) plays a key role in the photoperiodic regulation of flowering in Arabidopsis (Arabidopsis thaliana). Here, we study the role of the closest barley CO homologs, HvCO1 and HvCO2, in the long day-dependent control of flowering and their interactions with Ppd-H1 and VRN-H2. HvCO2 overexpression in spring barley, with a natural deletion of the VRN-H2 locus, caused a Ppd-H1-dependent induction of flowering and FLOWERING LOCUS T1 (HvFT1) expression. In winter barley, which carries the VRN-H2 locus, overexpression of HvCO1/CO2 caused an up-regulation of VRN-H2, resulting in a reduced expression of HvFT1 and delayed flowering under long- and short-day conditions. In addition, natural variation at Ppd-H1 altered the expression of VRN-H2 in wild-type plants under long days. VRN-H2, in turn, was involved in the down-regulation of Ppd-H1 and HvCO2, demonstrating strong reciprocal interactions between HvCO2, Ppd-H1, and VRN-H2. Consequently, this study showed that the induction of the floral repressor VRN-H2 and the floral activator HvFT1 was regulated by the same genes, Ppd-H1 and HvCO1/CO2. Our findings provide a novel insight into the photoperiodic regulation of the vernalization pathway in barley.

Photoperiod-H1 (Ppd-H1) Controls Leaf Size.

Leaf size is a major determinant of plant photosynthetic activity and biomass; however, it is poorly understood how leaf size is genetically controlled in cereal crop plants like barley (Hordeum vulgare). We conducted a genome-wide association scan for flowering time, leaf width, and leaf length in a diverse panel of European winter cultivars grown in the field and genotyped with a single-nucleotide polymorphism array. The genome-wide association scan identified PHOTOPERIOD-H1 (Ppd-H1) as a candidate gene underlying the major quantitative trait loci for flowering time and leaf size in the barley population. Microscopic phenotyping of three independent introgression lines confirmed the effect of Ppd-H1 on leaf size. Differences in the duration of leaf growth and consequent variation in leaf cell number were responsible for the leaf size differences between the Ppd-H1 variants. The Ppd-H1-dependent induction of the BARLEY MADS BOX genes BM3 and BM8 in the leaf correlated with reductions in leaf size and leaf number. Our results indicate that leaf size is controlled by the Ppd-H1- and photoperiod-dependent progression of plant development. The coordination of leaf growth with flowering may be part of a reproductive strategy to optimize resource allocation to the developing inflorescences and seeds.

Floral transitions in wheat and barley: interactions between photoperiod, abiotic stresses, and nutrient status.

The timing of plant reproduction has a large impact on yield in crop plants. Reproductive development in temperate cereals comprises two major developmental transitions. During spikelet initiation, the identity of the shoot meristem switches from the vegetative to the reproductive stage and spikelet primordia are formed on the apex. Subsequently, floral morphogenesis is initiated, a process strongly affected by environmental variation. Recent studies in cereal grasses have suggested that this later phase of inflorescence development controls floret survival and abortion, and is therefore crucial for yield. Here, we provide a synthesis of the early morphological and the more recent genetic studies on shoot development in wheat and barley. The review explores how photoperiod, abiotic stress, and nutrient signalling interact with shoot development, and pinpoints genetic factors that mediate development in response to these environmental cues. We anticipate that research in these areas will be important in understanding adaptation of cereal grasses to changing climate conditions.

Metabolite profiling of barley flag leaves under drought and combined heat and drought stress reveals metabolic QTLs for metabolites associated with antioxidant defense.

Barley (Hordeum vulgare L.) is among the most stress-tolerant crops; however, not much is known about the genetic and environmental control of metabolic adaptation of barley to abiotic stresses. We have subjected a genetically diverse set of 81 barley accessions, consisting of Mediterranean landrace genotypes and German elite breeding lines, to drought and combined heat and drought stress at anthesis. Our aim was to (i) investigate potential differences in morphological, physiological, and metabolic adaptation to the two stress scenarios between the Mediterranean and German barley genotypes and (ii) identify metabolic quantitative trait loci (mQTLs). To this end, we have genotyped the investigated barley lines with an Illumina iSelect 9K array and analyzed a set of 57 metabolites from the primary C and N as well as antioxidant metabolism in flag leaves under control and stress conditions. We found that drought-adapted genotypes attenuate leaf carbon metabolism much more strongly than elite lines during drought stress adaptation. Furthermore, we identified mQTLs for flag leaf γ-tocopherol, glutathione, and succinate content by association genetics that co-localize with genes encoding enzymes of the pathways producing these antioxidant metabolites. Our results provide the molecular basis for breeding barley cultivars with improved abiotic stress tolerance.

Fine mapping of a major QTL for awn length in barley using a multiparent mapping population.

KEY MESSAGE: Awn length was mapped using a multiparent population derived from cv. Morex and four wild accessions. One QTL was fine mapped and candidate genes were identified in NILs by RNA-seq. Barley awns are photosynthetically active and contribute to grain yield. Awn length is variable among both wild and cultivated barley genotypes and many mutants with alterations in awn length have been identified. Here, we used a multiparent mapping population derived from cv. Morex and four genetically diverse wild barley lines to detect quantitative trait loci (QTLs) for awn length. Twelve QTLs, distributed over the barley genome, were identified with the most significant one located on chromosome arm 7HL (QTL AL7.1). The effect of AL7.1 was confirmed using near isogenic lines (NILs) and fine-mapped in two independent heterogeneous inbred families to a < 0.9 cM interval. With exception of a small effect on grain width, no other traits such as plant height or flowering time were affected by AL7.1. Variant calling on transcripts obtained from RNA sequencing reads in NILs was used to narrow down the list of candidate genes located in the interval. This data may be used for further characterization and unravelling of the mechanisms underlying natural variation in awn length.

Mutation at the circadian clock gene EARLY MATURITY 8 adapts domesticated barley (Hordeum vulgare) to short growing seasons.

The circadian clock is an autonomous oscillator that produces endogenous biological rhythms with a period of about 24 h. This clock allows organisms to coordinate their metabolism and development with predicted daily and seasonal changes of the environment. In plants, circadian rhythms contribute to both evolutionary fitness and agricultural productivity. Nevertheless, we show that commercial barley varieties bred for short growing seasons by use of early maturity 8 (eam8) mutations, also termed mat-a, are severely compromised in clock gene expression and clock outputs. We identified EAM8 as a barley ortholog of the Arabidopsis thaliana circadian clock regulator EARLY FLOWERING3 (ELF3) and demonstrate that eam8 accelerates the transition from vegetative to reproductive growth and inflorescence development. We propose that eam8 was selected as barley cultivation moved to high-latitude short-season environments in Europe because it allowed rapid flowering in genetic backgrounds that contained a previously selected late-flowering mutation of the photoperiod response gene Ppd-H1. We show that eam8 mutants have increased expression of the floral activator HvFT1, which is independent of allelic variation at Ppd-H1. The selection of independent eam8 mutations shows that this strategy facilitates short growth-season adaptation and expansion of the geographic range of barley, despite the pronounced clock defect.