Functional and transcriptional characterization of a barley mutant with impaired photosynthesis.

Chemical mutagenesis induces variations that may assist in the identification of targets for adaptation to growth under atmospheric CO2 enrichment. The aim of this work was to characterize the limitations causing reduced photosynthetic capacity in G132 mutagenized barley (Hordeum vulgare L. cv. Graphic) grown in a glasshouse. Compared to the wild type (WT) G132 showed increased transcript levels for the PSII light harvesting complex, but lower levels of chlorophyll, transcripts for protochlorophyllide oxidoreductase A and psbQ, and PSII quantum efficiency in young leaves. Rubisco limitation had an overriding influence on G132 photosynthesis, and was due to strong and selective decreases in Rubisco protein and activity. These reductions were accompanied by enhanced Rubisco transcripts, but increased levels of a Rubisco degradation product. G132 showed lower levels of carbohydrates, amino acids and corresponding transcripts, and proteins, but not of nitrate. Many of the measured parameters recovered in the mutant as development progressed, or decreased less than in the WT, indicating that senescence was delayed. G132 had a longer growth period than the WT and similar final plant dry matter. The reduced resource investment in Rubisco of G132 may prove useful for studies on barley adaptation to elevated CO2 and climate change.

Photosynthesis-dependent/independent control of stomatal responses to CO2 in mutant barley with surplus electron transport capacity and reduced SLAH3 anion channel transcript.

The mechanisms of stomatal sensitivity to CO2 are yet to be fully understood. The role of photosynthetic and non-photosynthetic factors in stomatal responses to CO2 was investigated in wild-type barley (Hordeum vulgare var. Graphic) and in a mutant (G132) with decreased photochemical and Rubisco capacities. The CO2 and DCMU responses of stomatal conductance (gs), gas exchange, chlorophyll fluorescence and levels of ATP, with a putative transcript for stomatal opening were analysed. G132 had greater gs than the wild-type, despite lower photosynthesis rates and higher intercellular CO2 concentrations (Ci). The mutant had Rubisco-limited photosynthesis at very high CO2 levels, and higher ATP contents than the wild-type. Stomatal sensitivity to CO2 under red light was lower in G132 than in the wild-type, both in photosynthesizing and DCMU-inhibited leaves. Under constant Ci and red light, stomatal sensitivity to DCMU inhibition was higher in G132. The levels of a SLAH3-like slow anion channel transcript, involved in stomatal closure, decreased sharply in G132. The results suggest that stomatal responses to CO2 depend partly on the balance of photosynthetic electron transport to carbon assimilation capacities, but are partially regulated by the CO2 signalling network. High gs can improve the adaptation to climate change in well-watered conditions.

Evolutionary history of barley cultivation in Europe revealed by genetic analysis of extant landraces.

BACKGROUND: Understanding the evolution of cultivated barley is important for two reasons. First, the evolutionary relationships between different landraces might provide information on the spread and subsequent development of barley cultivation, including the adaptation of the crop to new environments and its response to human selection. Second, evolutionary information would enable landraces with similar traits but different genetic backgrounds to be identified, providing alternative strategies for the introduction of these traits into modern germplasm. RESULTS: The evolutionary relationships between 651 barley landraces were inferred from the genotypes for 24 microsatellites. The landraces could be divided into nine populations, each with a different geographical distribution. Comparisons with ear row number, caryopsis structure, seasonal growth habit and flowering time revealed a degree of association between population structure and phenotype, and analysis of climate variables indicated that the landraces are adapted, at least to some extent, to their environment. Human selection and/or environmental adaptation may therefore have played a role in the origin and/or maintenance of one or more of the barley landrace populations. There was also evidence that at least some of the population structure derived from geographical partitioning set up during the initial spread of barley cultivation into Europe, or reflected the later introduction of novel varieties. In particular, three closely-related populations were made up almost entirely of plants with the daylength nonresponsive version of the photoperiod response gene PPD-H1, conferring adaptation to the long annual growth season of northern Europe. These three populations probably originated in the eastern Fertile Crescent and entered Europe after the initial spread of agriculture. CONCLUSIONS: The discovery of population structure, combined with knowledge of associated phenotypes and environmental adaptations, enables a rational approach to identification of landraces that might be used as sources of germplasm for breeding programs. The population structure also enables hypotheses concerning the prehistoric spread and development of agriculture to be addressed.

Gene and QTL detection in a three-way barley cross under selection by a mixed model with kinship information using SNPs.

Quantitative trait locus (QTL) detection is commonly performed by analysis of designed segregating populations derived from two inbred parental lines, where absence of selection, mutation and genetic drift is assumed. Even for designed populations, selection cannot always be avoided, with as consequence varying correlation between genotypes instead of uniform correlation. Akin to linkage disequilibrium mapping, ignoring this type of genetic relatedness will increase the rate of false-positives. In this paper, we advocate using mixed models including genetic relatedness, or 'kinship' information for QTL detection in populations where selection forces operated. We demonstrate our case with a three-way barley cross, designed to segregate for dwarfing, vernalization and spike morphology genes, in which selection occurred. The population of 161 inbred lines was screened with 1,536 single nucleotide polymorphisms (SNPs), and used for gene and QTL detection. The coefficient of coancestry matrix was estimated based on the SNPs and imposed to structure the distribution of random genotypic effects. The model incorporating kinship, coancestry, information was consistently superior to the one without kinship (according to the Akaike information criterion). We show, for three traits, that ignoring the coancestry information results in an unrealistically high number of marker-trait associations, without providing clear conclusions about QTL locations. We used a number of widely recognized dwarfing and vernalization genes known to segregate in the studied population as landmarks or references to assess the agreement of the mapping results with a priori candidate gene expectations. Additional QTLs to the major genes were detected for all traits as well.

Molecular characterization of mlo mutants in North American two- and six-rowed malting barley cultivars.

SUMMARY Barley lines PRU1, URS1 and URS2 represent three candidate mlo mutants induced in either the two-rowed cultivar Prudentia or the six-rowed cultivar Ursula. Both Prudentia and Ursula are North American malting barley varieties with specific malting properties. Here, we analysed the three candidate mutants at the molecular level. We identified lesions in the Mlo gene of all three lines, causing either a premature stop codon (PRU1), a shift in the reading frame (URS1) or a single amino acid replacement (URS2). In a transient gene expression assay, the URS2 mlo allele fails to complement a barley null mutant genotype, indicating that URS2 is a genuine mlo mutant (here designated as mlo-33). The MLO-33 mutant variant accumulates to similar levels as the wild-type MLO protein in Arabidopsis protoplasts, suggesting that MLO-33 is stable in planta. We show that the mlo-33 allele can be readily detected in barley genomic DNA by a cleaved amplified polymorphic sequence marker, rendering this allele particularly suited for marker-assisted breeding.