Kirsten Kørup

Cytosolic glutamine synthetase is important for photosynthetic efficiency and water use efficiency in potato as revealed by high-throughput sequencing QTL analysis

Key messageWUE phenotyping and subsequent QTL analysis revealed cytosolic GS genes importance for limiting N loss due to photorespiration under well-watered and well-fertilized conditions.AbstractPotato (Solanum tuberosum L.) closes its stomata at relatively low soil water deficits frequently encountered in normal field conditions resulting in unnecessary annual yield losses and extensive use of artificial irrigation. Therefore, unraveling the genetics underpinning variation in water use efficiency (WUE) of potato is important, but has been limited by technical difficulties in assessing the trait on individual plants and thus is poorly understood. In this study, a mapping population of potatoes has been robustly phenotyped, and considerable variation in WUE under well-watered conditions was observed. Two extreme WUE bulks of clones were identified and pools of genomic DNA from them as well as the parents were sequenced and mapped to reference potato genome. Following a novel data analysis approach, two highly resolved QTLs were found on chromosome 1 and 9. Interestingly, three genes encoding isoforms of cytosolic glutamine synthase were located in the QTL at chromosome 1 suggesting a major contribution of this enzyme to photosynthetic efficiency and thus WUE in potato. Indeed, Glutamine synthetase enzyme activity of leaf extracts was measured and found to be correlated with contrasting WUE phenotypes.

Can miscanthus C4 photosynthesis compete with festulolium C3 photosynthesis in a temperate climate

Miscanthus, a perennial grass with C4 photosynthesis, is regarded as a promising energy crop due to its high biomass productivity. Compared with other C4 species, most miscanthus genotypes have high cold tolerances at 14 °C. However, in temperate climates, temperatures below 14 °C are common and our aim was to elucidate cold tolerances of different miscanthus genotypes and compare with a C3 perennial grass – festulolium. Eleven genotypes of M. sacchariflorus, M. sinensis, M. tinctorius, M. × giganteus as well as festulolium were grown under warm (24/20 °C, day/night) and three under cold (14/10 °C, 10/8 °C and 6/4 °C) conditions in a controlled environment. Measurements of photosynthetic light response curves, operating quantum yield of photosystem II (ΦPSII), net photosynthetic rate at a PAR of 1000 μmol m−2 s−1 (A1000) and dark‐adapted chlorophyll fluorescence (Fv/Fm) were made at each temperature. In addition, temperature response curves were measured after the plants had been grown at 6/4 °C. The results showed that two tetraploid M. sacchariflorus and the standard triploid M. × giganteus cv. Hornum retained a significantly higher photosynthetic capacity than other miscanthus genotypes at each temperature level and still maintained photosynthesis after growing for a longer period at 6/4 °C. Only two of five measured miscanthus genotypes increased photosynthesis immediately after the temperature was raised again. The photosynthetic capacity of festulolium was significantly higher at 10/8 °C and 6/4 °C than of miscanthus genotypes. This indicates that festulolium may be more productive than the currently investigated miscanthus genotypes in cool, maritime climates. Within miscanthus, only one M. sacchariflorus genotype exhibited the same photosynthetic capacity as Hornum at both cold conditions and when the temperature was raised again. Therefore, this genotype could be useful for breeding new varieties with an improved cold tolerance vis‐a‐vis Hornum, and be valuable in broadening the genetic diversity of miscanthus for more widespread cultivation in temperate climates.

Next Generation Sequencing Bulk Segregant Analysis of Potato Support that Differential Flux into the Cholesterol and Stigmasterol Metabolite Pools Is Important for Steroidal Glycoalkaloid Content

Potatoes and other Solanaceae species produce biologically active secondary metabolites called steroidal glycoalkaloids (GAs) which have antimicrobial, fungicidal, antiviral and insecticidal properties. GAs are, however, also toxic to animals and humans. Compared to wild species of potato, the elite cultivars primarily used for everyday consumption have very low contents of GAs. Breeding for important agronomical traits, like e.g. pathogen resistance, often requires the use of wild species and a situation where offspring have unacceptable high contents of GAs quite frequently arises. Knowledge of metabolic pathways leading to the synthesis of GAs, as well as of the genes that are responsible for the observed differences in plant and tuber GA content is only partial. The primary purpose of this study was to identify genomic regions and candidate genes responsible for differential GA content within a diploid potato mapping population (n = 90) that shows a high variation in GA accumulation. The analysis was performed using a novel method based on next generation genome sequencing. A region on chromosome 1 was found to be associated with differential GA content. Within that region, sterol 24-C-methyltransferase (SMT1), sterol desaturase (SD) and C-4 sterol methyl oxidase (SMO) genes were found, all encoding critical enzymes in the synthesis of the GAs precursor cholesterol.

Screening for intrinsic water use efficiency in a potato dihaploid mapping population under progressive drought conditions

A drought screening experiment focusing on intrinsic water use efficiency (WUEi) was carried out among 132 clones belonging to a dihaploid potato mapping population. The clones were exposed to progressive soil drying during a five-day period in a greenhouse pot experiment. Analysis of the underlying variables was done based on a multivariate data analysis strategy. The strategy successfully divided the clones into WUEi performance categories. Differences between clonal WUEi responses were traced back to differences in the net photosynthetic rate. Stomatal conductance (gs) did not vary significantly between the clones. Leaf abscisic acid (ABA) concentration and leaf water potential were found to reflect known isohydric behaviour for potato, and a non-linear relationship could be established for gs and leaf ABA concentration across the WUEi groups. Similarly, a common non-linear relationship between leaf ABA concentration and soil water potential was found. The latter findings suggest that the investigated population did not harbour significant genetic variation as to ABA production as function of soil desiccation level or with respect to the sensitivity of stomatal aperture vis-à-vis leaf ABA concentration and soil water potential.

Low-temperature leaf photosynthesis of a Miscanthus germplasm collection correlates positively to shoot growth rate and specific leaf area.

Background and Aims The C4 perennial grass miscanthus has been found to be less sensitive to cold than most other C4 species, but still emerges later in spring than C3 species. Genotypic differences in miscanthus were investigated to identify genotypes with a high cold tolerance at low temperatures and quick recovery upon rising temperatures to enable them to exploit the early growing season in maritime cold climates. Suitable methods for field screening of cold tolerance in miscanthus were also identified. Methods Fourteen genotypes of M. sacchariflorus, M. sinensis, M. tinctorius and M. × giganteus were selected and grown under warm (24 °C) and cold (14 °C) conditions in a controlled environment. Dark-adapted chlorophyll fluorescence, specific leaf area (SLA) and net photosynthetic rate at a photosynthetically active radiation (PAR) of 1000 μmol m–2 s–1 (A1000) were measured. Photosynthetic light and CO2 response curves were obtained from 11 of the genotypes, and shoot growth rate was measured under field conditions. Key Results A positive linear relationship was found between SLA and light-saturated photosynthesis (Asat) across genotypes, and also between shoot growth rate under cool field conditions and A1000 at 14 °C in a climate chamber. When lowering the temperature from 24 to 14 °C, one M. sacchariflorus exhibited significantly higher Asat and maximum photosynthetic rate in the CO2 response curve (Vmax) than other genotypes at 14 °C, except M. × giganteus ‘Hornum’. Several genotypes returned to their pre-chilling A1000 values when the temperature was increased to 24 °C after 24 d growth at 14 °C. Conclusions One M. sacchariflorus genotype had similar or higher photosynthetic capacity than M. × giganteus, and may be used for cultivation together with M. × giganteus or for breeding new interspecies hybrids with improved traits for temperate climates. Two easily measured variables, SLA and shoot growth rate, may be useful for genotype screening of productivity and cold tolerance.

Biomass production and water use efficiency in perennial grasses during and after drought stress

Drought is a great challenge to agricultural production, and cultivation of drought‐tolerant or water use‐efficient cultivars is important to ensure high biomass yields for bio‐refining and bioenergy. Here, we evaluated drought tolerance of four C3 species, Dactylis glomerata cvs. Sevenop and Amba, Festuca arundinacea cvs. Jordane and Kora, Phalaris arundinacea cvs. Bamse and Chieftain and Festulolium pabulare cv. Hykor, and two C4 species Miscanthus × giganteus and M. lutarioriparius. Control (irrigated) and drought‐treated plants were grown on coarse and loamy sand in 1 m2 lysimeter plots where rain was excluded. Drought periods started after harvest and lasted until 80% of available soil water had been used. Drought caused a decrease in dry matter yield (DM; P < 0.001) for all species and cultivars during the drought period. Cultivars Sevenop, Kora and Jordane produced DM at equal levels and higher than the other C3 cultivars in control and drought‐treated plots both during and after the drought period. Negative correlations were observed between stomatal conductance (gs) and leaf water potential (P < 0.01) and positive correlations between gs and DM (P < 0.05) indicating that gs might be suitable for assessment of drought stress. There were indications of positive associations between plants carbon isotope composition and water use efficiency (WUE) as well as DM under well‐watered conditions. Compared to control, drought‐treated plots showed increased growth in the period after drought stress. Thus, the drought events did not affect total biomass production (DMtotal) of the whole growing season. During drought stress and the whole growing season, WUE was higher in drought‐treated compared to control plots, so it seems possible to save water without loss of biomass. Across soil types, M. lutarioriparius had the highest DMtotal (15.0 t ha−1), WUEtotal (3.6 g L−1) and radiation use efficiency (2.3 g MJ−1) of the evaluated grasses.