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.Flowering is one of the most critical stages in the life cycle of plants. The coincidence of flowering with favorable conditions ensures that seed production is maximized and enhances the chances of successful reproduction. A key adaptive mechanism to achieve this coincidence is sensing changes in daylength or photoperiod (Greenup et al., 2009). Long photoperiods promote flowering in the model and facultative long-day (LD) plant Arabidopsis (Arabidopsis thaliana) through the activity of CONSTANS (CO), a transcription factor that binds to the promotor of FLOWERING LOCUS T (FT), which, in turn, induces the floral transition (Putterill et al., 1995;Tiwari et al., 2010). CO encodes a protein with two zinc finger B-boxes and a CCT (CONSTANS, CONSTANS-like, and TIMING OF CAB EXPRESSION1 [TOC1]) domain (Robson et al., 2001). CO transcription is regulated by the circadian clock and its components in a way that allows the accumulation of CO mRNA at the end of the light period of long days (LDs) but after dusk in short days (SDs; Imaizumi et al., 2005;Fornara et al., 2009). The CO protein is stabilized by photoreceptors in the light and degraded by the ubiquitin ligase CONSTITUTIVE PHOTOMORPHO-GENIC1 during the dark, which allows the accumulation of CO at the end of a long day to induce FT transcription (Jang et al., 2008;Turck et al., 2008).The function of CO in controlling the photoperiod response is conserved in the short-day (SD) cereal monocot rice (Oryza sativa). Under inductive SDs, Heading date1 (Hd1), the rice ortholog of CO, promotes flowering by inducing the expression of Hd3a, ...

Spring growth in barley controlled by natural variation at Vrn-H1 and Vrn-H2 improved yield stability in marginal Syrian environments. The objective of the present study was to identify QTL influencing agronomic performance in rain-fed Mediterranean environments in a recombinant inbred line (RIL) population, ARKE derived from the Syrian barley landrace, Arta and the Australian feed cultivar, Keel. The population was field tested for agronomic performance at two locations in Syria for 4 years with two sowing dates, in autumn and winter. Genotypic variability in yield of the RIL population was mainly affected by year-to-year variation presumably caused by inter-annual differences in rainfall distribution. The spring growth habit and early flowering inherited from the Australian cultivar Keel increased plant height and biomass and improved yield stability in Syrian environments. QTL for yield and biomass coincided with the map location of flowering time genes, in particular the vernalisation genes Vrn-H1 and Vrn-H2. In marginal environments with terminal drought, the Vrn-H1 allele inherited from Keel improved final biomass and yield. Under changing climate conditions, such as shorter winters, reduced rainfall, and early summer drought, spring barley might thus outperform the traditional vernalisation-sensitive Syrian landraces. We present the ARKE population as a valuable genetic resource to further elucidate the genetics of drought adaptation of barley in the field.

In many angiosperm plants, ()-like genes have duplicated and functionally diverged to control different reproductive traits or stages. Barley () carries several -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 accelerated the initiation of spikelet primordia and the early reproductive development of spring barley independently of the photoperiod. However, 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 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 () 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 (), (), and Understanding the specific functions of individual-like genes will allow modification of individual phases of preanthesis development and thereby adaptation to different environments and improved yield.

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M.A.M.); 0000-0001-7086-5470 (J.Z.); 0000-0002-6816-586X (M.v.K.).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.