M. Pilar Gracia

Expression analysis of vernalization and day-length response genes in barley (Hordeum vulgare L.) indicates that VRNH2 is a repressor of PPDH2 (HvFT3) under long days

The response to vernalization and the expression of genes associated with responses to vernalization (VRNH1, VRNH2, and VRNH3) and photoperiod (PPDH1 and PPDH2) were analysed in four barley (Hordeum vulgare L.) lines: ‘Alexis’ (spring), ‘Plaisant’ (winter), SBCC058, and SBCC106 (Spanish inbred lines), grown under conditions of vernalization and short days (VSD) or no vernalization and long days (NVLD). The four genotypes differ in VRNH1. Their growth habits and responses to vernalization correlated with the level of expression of VRNH1 and the length of intron 1. ‘Alexis’ and ‘Plaisant’ behaved as expected. SBCC058 and SBCC106 showed an intermediate growth habit and flowered relatively late in the absence of vernalization. VRNH1 expression was induced by cold for all genotypes. Under VSD, VRNH1 expression was detected in the SBCC genotypes later than in ‘Alexis’ but earlier than in ‘Plaisant’. VRNH2 was repressed under short days while VRNH1 expression increased in parallel. VRNH3 was detected only in ‘Alexis’ under NVLD, whereas it was not expressed in plants with the active allele of VRNH2 (SBCC058 and ‘Plaisant’). Under VSD, PPDH2 was expressed in ‘Alexis’, SBCC058, and SBCC106, but it was only expressed weakly in ‘Alexis’ under NVLD. Further analysis of PPDH2 expression in two barley doubled haploid populations revealed that, under long days, HvFT3 and VRNH2 expression levels were related inversely. The timing of VRNH2 expression under a long photoperiod suggests that this gene might be involved in repression of PPDH2 and, indirectly, in the regulation of flowering time through an interaction with the day-length pathway.

Adaptation of barley to mild winters: A role for PPDH2

BackgroundUnderstanding the adaptation of cereals to environmental conditions is one of the key areas in which plant science can contribute to tackling challenges presented by climate change. Temperature and day length are the main environmental regulators of flowering and drivers of adaptation in temperate cereals. The major genes that control flowering time in barley in response to environmental cues are VRNH1, VRNH2, VRNH3, PPDH1, and PPDH2 (candidate gene HvFT3). These genes from the vernalization and photoperiod pathways show complex interactions to promote flowering that are still not understood fully. In particular, PPDH2 function is assumed to be limited to the ability of a short photoperiod to promote flowering. Evidence from the fields of biodiversity, ecogeography, agronomy, and molecular genetics was combined to obtain a more complete overview of the potential role of PPDH2 in environmental adaptation in barley.ResultsThe dominant PPDH2 allele is represented widely in spring barley cultivars but is found only occasionally in modern winter cultivars that have strong vernalization requirements. However, old landraces from the Iberian Peninsula, which also have a vernalization requirement, possess this allele at a much higher frequency than modern winter barley cultivars. Under field conditions in which the vernalization requirement of winter cultivars is not satisfied, the dominant PPDH2 allele promotes flowering, even under increasing photoperiods above 12 h. This hypothesis was supported by expression analysis of vernalization-responsive genotypes. When the dominant allele of PPDH2 was expressed, this was associated with enhanced levels of VRNH1 and VRNH3 expression. Expression of these two genes is needed for the induction of flowering. Therefore, both in the field and under controlled conditions, PPDH2 has an effect of promotion of flowering.ConclusionsThe dominant, ancestral, allele of PPDH2 is prevalent in southern European barley germplasm. The presence of the dominant allele is associated with early expression of VRNH1 and early flowering. We propose that PPDH2 promotes flowering of winter cultivars under all non-inductive conditions, i.e. under short days or long days in plants that have not satisfied their vernalization requirement. This mechanism is indicated to be a component of an adaptation syndrome of barley to Mediterranean conditions.

Joint analysis for heading date QTL in small interconnected barley populations

The purpose of the present work is to validate the effect of the main QTL determining heading date in a set of 281 doubled haploid lines of barley, derived from 17 small interconnected populations, whose parents are cultivars commonly used in the Spanish barley breeding program. We used 72 molecular markers distributed across the seven chromosomes, particularly in regions known to contain flowering time genes or QTL. A combined linkage map over the 17 populations was constructed. The lines were evaluated in four field trials: two autumn sowings and two winter sowings, and in two treatments at a greenhouse trial, under controlled conditions of photoperiod and temperature. We have found that it is possible to carry out QTL detection in a complex germplasm set, representative of the materials used in an active breeding programme. In most cases two alleles per QTL were detected, though polymorphism of flanking markers was notably higher. The results revealed that there is a set of QTL that accounts for an important percentage of the phenotypic variation, suitable for marker assisted selection. Also, the role of the regions carrying the photoperiod response genes Ppd-H1 and Ppd-H2, the vernalization response genes Vrn-H1 and Vrn-H2, and the earliness per se locus Eam6, of which allele-specific or closely linked markers were available, was confirmed. These results support the use of this kind of approach for the validation of QTL found in single cross population studies, or to survey allelic diversity in plant breeding sets of materials.

Introgression of an intermediate VRNH1 allele in barley (Hordeum vulgare L.) leads to reduced vernalization requirement without affecting freezing tolerance

The process of vernalization is mainly controlled by two genes in winter barley (Hordeum vulgare L.), VRNH1 and VRNH2. A recessive allele at VRNH1 and a dominant allele at VRNH2 must be present to induce a vernalization requirement. In addition, this process is usually associated with greater low-temperature tolerance. Spanish barleys originated in areas with mild winters and display a reduced vernalization requirement compared with standard winter cultivars. The objective of this study was to investigate the genetic origin of this reduced vernalization requirement and its effect on frost tolerance. We introgressed the regions of a typical Spanish barley line that carry VRNH1 and VRNH2 into a winter cultivar, Plaisant, using marker-assisted backcrossing. We present the results of a set of 12 lines introgressed with all four possible combinations of VRNH1 and VRNH2, which were evaluated for vernalization requirement and frost tolerance. The reduced vernalization requirement of the Spanish parent was confirmed, and was found to be due completely to the effect of the VRNH1 region. The backcross lines showed no decline in frost tolerance compared with that of the recurrent parent unless they carried an extra segment of chromosome 5H. This extra segment, a carryover of the backcross process, apparently contained the well-known frost tolerance quantitative trait locus Fr-H2. We demonstrate that it is possible to manipulate the vernalization requirement with only minor effects on frost tolerance. This finding opens the path to creating new types of barley cultivars that are better suited to specific environments, especially in a climate-change scenario.

HvFT1 polymorphism and effect—survey of barley germplasm and expression analysis

Flowering time in plants is a tightly regulated process. In barley (Hordeum vulgare L.), HvFT1, ortholog of FLOWERING LOCUS T, is the main integrator of the photoperiod and vernalization signals leading to the transition from vegetative to reproductive state of the plant. This gene presents sequence polymorphisms affecting flowering time in the first intron and in the promoter. Recently, copy number variation (CNV) has been described for this gene. An allele with more than one copy was linked to higher gene expression, earlier flowering, and an overriding effect of the vernalization mechanism. This study aims at (1) surveying the distribution of HvFT1 polymorphisms across barley germplasm and (2) assessing gene expression and phenotypic effects of HvFT1 alleles. We analyzed HvFT1 CNV in 109 winter, spring, and facultative barley lines. There was more than one copy of the gene (2–5) only in spring or facultative barleys without a functional vernalization VrnH2 allele. CNV was investigated in several regions inside and around HvFT1. Two models of the gene were found: one with the same number of promoters and transcribed regions, and another with one promoter and variable number of transcribed regions. This last model was found in Nordic barleys only. Analysis of HvFT1 expression showed that association between known polymorphisms at the HvFT1 locus and the expression of the gene was highly dependent on the genetic background. Under long day conditions the earliest flowering lines carried a sensitive PpdH1 allele. Among spring cultivars with different number of copies, no clear relation was found between CNV, gene expression and flowering time. This was confirmed in a set of doubled haploid lines of a population segregating for HvFT1 CNV. Earlier flowering in the presence of several copies of HvFT1 was only seen in cultivar Tammi, which carries one promoter, suggesting a relation of gene structure with its regulation. HvCEN also affected to a large extent flowering time.

Identification of quantitative trait loci for agronomic traits contributed by a barley (Hordeum vulgare) Mediterranean landrace

Abstract. Some Spanish barley (Hordeum vulgare L.) landraces perform better than modern cultivars at low-production sites. The objective of this study was to identify favourable quantitative trait loci (QTLs) for interesting agronomic traits contributed by the landrace SBCC073. To achieve this objective, a population of 100 BC1F5 lines was derived from the cross between the elite cultivar Orria, with high productivity, and the Spanish landrace SBCC073, which was the best performer in low-production trials. The population was evaluated in field trials for 3 years (2011, 2013, and 2014) in Zaragoza, Spain. The population was genotyped with a DArTseq genotyping-by-sequencing assay. A genetic linkage map was developed by using markers of four flowering-time genes and 1227 single-nucleotide polymorphisms of good quality. The genetic map resulted in 11 linkage groups, covering a total distance of 871.1 cM. Five QTLs for grain yield were detected on 2H.1, 4H, 5H and 6H.2. Alleles from SBCC073 contributed to increased yield in three of them. A region at the end of chromosome 5H contains favourable alleles for early vigour, higher grain yield and earlier flowering, all derived from SBCC073. Alleles from Orria contributed to increasing grain yield and simultaneously to reducing plant height on the same region of 6H.2, and to increasing 1000-kernel weight on chromosomes 3H and 5H.

Barley Adaptation: Teachings from Landraces Will Help to Respond to Climate Change

Adaptation of crops to temperate climates depends to a large extent on plants having the appropriate combination of genes to respond to day length and temperature. Global warming poses new challenges to plant breeding. In many places, current cultivars will no longer be suited for cultivation. To sustain agricultural production, future cultivars must be provided with genes that ensure optimum adaptation to the new conditions. We present several findings on barley adaptation to Mediterranean climates, published over the last years, which resulted from the study of adaptations exhibited by local landraces.