Identification of quantitative trait loci (QTL) for drought tolerance and leaf senescence in juvenile barley

Im Rahmen des Klimawandels kommt der Toleranz gegenüber Trockenstress eine steigende Bedeutung zu. Durch die durch Trockenstress ausgelöste frühzeitige Blattseneszenz kommt es zu einem Abbruch der Photosynthese und frühzeitig zu Umlagerungsprozessen von gespeicherten Assimilaten in das Korn. Da eine Phänotypisierung auf Trockenstress und Seneszenz in den Züchtungsprozess der Gerste nur schwer zu integrieren ist, sind arkergestützte Selektionsverfahren von Vorteil. Ziel dieser Arbeit war es daher, mittels genomweiter Assoziationsstudien (GWAS) Marker zu identifizieren, die mit Trockenstress-, oder Blattseneszenzparametern in juveniler Gerste assoziiert sind. Für die Phänotypisierung hinsichtlich der Reaktion auf Trockenstress und dadurch induzierter Blattseneszenz, wurde ein Screening- Verfahren entwickelt, welches eine verlässliche Erfassung dieser Merkmale erlaubt. 156 Wintergerstengenotypen wurden in frühen Entwicklungsstadien im Gewächshaus unter Kontroll- und Stressbedingungen analysiert. Die Trockenstressapplikation erfolgte vom Primärblattstadium für 4 Wochen. In diesen Versuchen wurden sechs physiologische Merkmale erfasst (Biomasse, Blattfarbe, Elektronentransportrate am Photosystem II, Osmolalität, Gehalt an freien Prolin und der Gesamtgehalt an löslichen Zuckern), sowie Expressionsstudien für Gene welche in die Trockenstressreaktion bzw. die Seneszenz involviert sind, durchgeführt. Für diese Merkmale und die Expression der 14 ausgewählten Gene konnten signifikante Genotypund Behandlungseffekte nachgewiesen werden. Anhand dieser Daten und 3.212 SNP Markern des Illumina 9k iSelect Chips wurden GWAS durchgeführt, um Genomregionen (QTL und eQTL) zu lokalisieren. Insgesamt konnten für die physiologischen Merkmale 47 QTL für die Reaktion auf Trockenstress, und weiterhin 15 eQTL identifiziert werden. Dabei wurden zwei Haupt- QTL-Regionen auf Chromosom 2H bei 50 cM und 5H bei 45 cM lokalisiert, in denen einige QTL für unterschiedliche Parameter, wie Biomasse und Blattfarbe nachgewiesen wurden. In diesen QTL-Regionen wurden Proteine identifiziert, die im Zusammenhang mit Trockenstress und Blattseneszenz stehen. Vier der regulierenden Gene zeigten eine differentielle Expression und es wurden entsprechend eQTL identifiziert. Ein eQTL für TRIUR3 stimmte mit dem, mittels phänotypischer Daten identifizierten QTL auf Chromosom 5H überein. Die assoziierten Marker BOPA1_9766-787 und SCRI_RS_102075 können nach Validierung geeignete Marker für eine Selektion auf Trockenstresstoleranz und Blattseneszenz in der Gerstenzüchtung darstellen.Drought stress as a trait with increasing importance in the background of climate change is an important factor limiting barley yield. Induced by drought, leaf senescence may occur prematurely, leading to a stop of photosynthesis and to an early translocation of stored assimilates into grains. For barley breeding, the identification of quantitative trait loci (QTL) involved in drought stress and leaf senescence may be an advantage as reliable phenotyping for drought stress is difficult to achieve. Therefore, the aim of the present thesis was to identify markers associated to drought stress response and drought stress induced leaf senescence in juvenile barley through genome wide association studies (GWAS), which will facilitate efficient marker based selection procedures. In a first step, a screening method was developed for analysing drought stress response and early leaf senescence in juvenile barley. Next, in semi controlled greenhouse pot experiments 156 winter barley genotypes were analysed in early developmental stages under control and drought stress treatment. Drought application started at the primary leaf stage and continued for a four weeks stress period. These experiments were used for phenotyping six physiological parameters (biomass yield, leaf colour, electron transport rate at photosystem II, osmolality, content of free proline and total content of soluble sugars), as well as for gene expression analysis of genes involved in drought stress and leaf senescence. Significant genotypic and treatment effects were detected for all phenotypic traits and gene expression data. Based on these data and on 3,212 SNP markers of the Illumina 9k iSelect Chip, GWAS were conducted to detect QTL and expression QTL (eQTL). In total, 47 significant QTL were identified for the traits analysed under drought stress conditions and 15 significant eQTL were found for the relative expression of the 14 genes involved in these traits. Under drought stress conditions, two major QTL regions overlapping for different traits such as biomass yield and leaf colour were detected on chromosome 2H at 50 cM and on chromosome 5H at 45 cM. In these QTL, genes coding for proteins involved in drought stress or leaf senescence were identified. Four of these genes showed a differential expression and thus, eQTL were detected. One eQTL for TRIUR3 coincides with the phenotypic QTL on chromosome 5H. After validation respective markers BOPA1_9766-787 and SCRI_RS_102075 may be used in future barley breeding programmes for improving tolerance to drought stress and leaf senescence

The barley HvSTP13GR mutant triggers resistance against biotrophic fungi

High-yielding and stress-resistant crops are essential to ensure future food supply. Barley is an important crop to feed livestock and to produce malt, but the annual yield is threatened by pathogen infections. Pathogens can trigger an altered sugar partitioning in the host plant, which possibly leads to an advantage for the pathogen. Hampering these processes represents a promising strategy to potentially increase resistance. We analysed the response of the barley monosaccharide transporter HvSTP13 towards biotic stress and its potential use for plant protection. The expression of HvSTP13 increased on bacterial and fungal pathogen-associated molecular pattern (PAMP) application, suggesting a PAMP-triggered signalling that converged on the transcriptional induction of the gene. Promoter studies indicate a region that is probably targeted by transcription factors downstream of PAMP-triggered immunity pathways. We confirmed that the nonfunctional HvSTP13GR variant confers resistance against an economically relevant biotrophic rust fungus in barley. Our experimental setup provides basal prerequisites to further decode the role of HvSTP13 in response to biological stress. Moreover, in line with other studies, our experiments indicate that the alteration of sugar partitioning pathways, in a host–pathogen interaction, is a promising approach to achieve broad and durable resistance in plants

Identification of genomic regions involved in tolerance to drought stress and drought stress induced leaf senescence in juvenile barley

BACKGROUND: Premature leaf senescence induced by external stress conditions, e.g. drought stress, is a main factor for yield losses in barley. Research in drought stress tolerance has become more important as due to climate change the number of drought periods will increase and tolerance to drought stress has become a goal of high interest in barley breeding. Therefore, the aim is to identify quantitative trait loci (QTL) involved in drought stress induced leaf senescence and drought stress tolerance in early developmental stages of barley (Hordeum vulgare L.) by applying genome wide association studies (GWAS) on a set of 156 winter barley genotypes. RESULTS: After a four weeks stress period (BBCH 33) leaf colour as an indicator of leaf senescence, electron transport rate at photosystem II, content of free proline, content of soluble sugars, osmolality and the aboveground biomass indicative for drought stress response were determined in the control and stress variant in greenhouse pot experiments. Significant phenotypic variation was observed for all traits analysed. Heritabilities ranged between 0.27 for osmolality and 0.61 for leaf colour in stress treatment and significant effects of genotype, treatment and genotype x treatment were estimated for most traits analysed. Based on these phenotypic data and 3,212 polymorphic single nucleotide polymorphisms (SNP) with a minor allele frequency >5 % derived from the Illumina 9 k iSelect SNP Chip, 181 QTL were detected for all traits analysed. Major QTLs for drought stress and leaf senescence were located on chromosome 5H and 2H. BlastX search for associated marker sequences revealed that respective SNPs are in some cases located in proteins related to drought stress or leaf senescence, e.g. nucleotide pyrophosphatase (AVP1) or serine/ threonin protein kinase (SAPK9). CONCLUSIONS: GWAS resulted in the identification of many QTLs involved in drought stress and leaf senescence of which two major QTLs for drought stress and leaf senescence were located on chromosome 5H and 2H. Results may be the basis to incorporate breeding for tolerance to drought stress or leaf senescence in barley breeding via marker based selection procedures. ELECTRONIC SUPPLEMENTARY MATERIAL: The online version of this article (doi:10.1186/s12870-015-0524-3) contains supplementary material, which is available to authorized users