The production of cereal crops is increasingly influenced by heat and drought stress. Despite the typical small-scale sub-regional variability of these stresses, impacts on yields are also of concern at larger regional to ...

The cereal cyst nematode Heterodera filipjevi is an important plant parasite causing substantial yield loss in wheat. The use of resistant cultivars is the preferable method to manage this nematode, however, only few resistance sources are identified in cereals and no durable resistant cultivar is available for H. filipjevi in wheat. In this study, a collection of 290 winter wheat accessions was screened for resistance against H. filipjevi. The plants were infected with nematode juveniles and the number of developing females and cysts was counted. One percent of the wheat accessions was ranked as resistant, 16% as moderately resistant, 41% as moderately susceptible, 26% as susceptible, and 15% as highly susceptible. To understand the underlying resistance mechanism, nematode invasion, development, and reproduction were analyzed in one resistant accession Nudakota and three moderately resistant accessions Ekonomka, Katea and Lantian 12 and compared with susceptible accession Bezostaya 1. Invasion rate, and number of females and cysts per plant were significantly lower in Nudakota, Ekonomka, Katea and Lantian 12 compared to Bezostaya 1. The different responses of wheat accessions observed in this study suggested genetic variation within the screened population. Therefore, it was decided to identify relevant quantitative trait loci (QTLs) and genes using genome-wide association studies. Association mapping is a powerful approach to detect associations between phenotypic variation and genetic polymorphisms; in this way favorable traits such as nematode resistance can be located in the genome. A mapping panel of 161 wheat accessions was genotyped by 90K iSelect SNP bead chip and was analyzed for QTL identification. These accessions were phenotyped in two nematode infection assays under controlled conditions. High variation was revealed in single nucleotide polymorphisms (SNPs) on wheat genomes A, B, and D. Linkage disequilibrium decayed across wheat genome was < 3cM. Population structure and principle component analysis (PCA) revealed a very low genetic differentiation (K = 2, and PCA1 = 6.16%) within the 161 wheat accessions and needed no further corrections. Eleven novel quantitative trait loci (QTLs) on chromosomes 1AL, 2AS, 2BL, 3AL, 3BL, 4AS, 4AL, 5BL and 7BL were detected using a mixed linear model at false discovery rate (P ≤ 0.01) that explained 43% of total genetic variation. The identified 11 novel QTLs can now be used in resistance breeding via marker-assisted selection. In-silico annotation of flanking sequences of the significant markers identified genes supposed to be involved in biotic and abiotic stresses. Eight of the 11 QTLs on chromosome 1AL, 2AS, 2BL, 3AL and 4AL were linked to putative genes known to be involved in plant-pathogen interactions. Two other QTLs on 3BL and one QTL on 7BL linked to putative genes known to be involved in abiotic stress and plant growth. Five of the QTLs identified on chromosomes 1AL, 2AS, 2BL, 3BL, and 5BL in this study were previously reported to be linked to resistance against H. avenae, while QTL IWB66494 on chromosome 2BL was reported to be linked to resistance against Fusarium head blight. Although the wheat genome is sequenced, annotation of a large number of genes and proteins is still limited. In order to characterize the candidate gene TaAAT we applied a comparative genomics approach and identified the orthologue gene AtAAP6 in Arabidopsis thaliana. Nematode infection assays of an AtAAP6 mutant Arabidopsis line revealed a significant reduction in average number of females, female size, and female-associated syncytia. Different methods showed that AtAAP6 is upregulated in syncytia. We also found a strong expression of TaAAT in infected roots of two susceptible wheat accessions, whereas the expression remained unchanged in infected roots of two resistant accessions. We further analyzed the amino acid sequence of AtAAP6 in 3 lowly susceptible and 3 highly susceptible Arabidopsis accessions and found glycine is substituted by alanine on a specific site in the AtAAP ORF in the lowly susceptible accessions. The molecular mechanism by which the exchange of a single amino acid in AtAAP6 leads to reduced nematode development needs further investigation....

In Nepal, the share of biomass in total energy consumption is about 88 % and of biomass for cooking and heating about 90 % in 76 % of the households. Fuelwood, crop residues and dung are the three main biomass types. The ...

The predicted climate change for North West Europe, which will be characterized by higher temperatures and lower rainfall during the summer months, will challenge future food production. Against this background, the question ...

The oxidative burst, production of Reactive Oxygen Species (ROS) in response to pathogen attack, is an important component of plant defence mechanisms. It is now generally recognised that the major source of ROS during an “oxidative burst” in plants is plasma membrane-bound NADPH oxidase. Plant NADPH oxidases have been named as respiratory burst oxidase homolog (Rboh) and possess six transmembrane-spanning domains corresponding to the domains that have been identified in the gp91^phox subunit in mammals. Genetic analysis of plants disrupted in Rboh functions suggested that they are required for the production of a full oxidative burst in response to a variety of pathogens. Yet, this lack of ROS production by NADPH oxidase has variable effects on plant responses to pathogens in terms of cell death and resistance. On one hand, it is positively correlated with plant resistance by strengthening of cell walls via cross linking, lipid peroxidation, membrane damage and activation of defence genes. On the other hand, it is an important susceptibility factor for successful infection of plants by various pathogens. Nevertheless, the mechanistic details on the pathosystem-specific role of Rboh-mediated ROS are not yet known. <br />Heterodera schachtii is a cyst nematode that establishes a long-term biotrophic relationship with the roots of sugar beets and brassicaceaous plants, including Arabidopsis thaliana. Infective stage juveniles of cyst nematodes (J2s) invade the roots and move towards the vascular cylinder where they establish a syncytial nurse cell system. The syncytium is the only source of nutrients for nematodes throughout their life-span of several weeks. This thesis focuses on the characterization of the role of Rboh-mediated ROS in plant-nematode interactions using the Arabidopsis thaliana – H. schachtii model system. <br /> In Arabidopsis, Rboh is encoded by ten genes (RbohA-RbohJ). We used loss-of-function mutants for Rboh genes and found that the number of female nematodes, the size of female nematodes, and the size of female-associated syncytium decreased greatly in rbohD and rbohD/F, but not in rbohA, rbohB, rbohC, rbohE, rbohF, rbohG, rbohH and rbohJ plants compared with Col-0 plants. A detailed microscopic, molecular and biochemical analysis showed that Rboh-dependent ROS are not required for root invasion; however, the syncytial establishment and development is impaired in the absence of ROS. To understand the mechanism underlying the Rboh-mediated reduced susceptibility to nematodes, we performed a genome-wide comparative transcriptome analysis between Col-0 and rbohD/F during early stages of infection. The gene that was most strongly downregulated encodes the vacuolar auxin transporter, Walls Are Thin 1 (WAT1). Genetic disruption of WAT1 led to similar changes in nematode susceptibility as in rbohD/F, thus suggesting that Rboh-mediated reduction in susceptibility to nematode is dependent on WAT1. Interestingly, both rbohD/F and wat1 are impaired in expression of key metabolic genes for indole metabolism including auxin biosynthesis upon nematode infection. In summary, our work provides for the first time a link between Rboh-mediated phenotypes and auxin metabolism. These data are the basis for a mechanistic understanding on the role of ROS as signals to promote nematode and other pathogen infections....

MicroRNAs (miRNAs), a class of short non-coding RNA molecules, emerged as major regulators of ~60% of all protein encoding genes. These molecules play an important role in mammalian follicular growth and embryonic development ...

Eggshell temperature is a critical factor, which can possibly influence immediate and/or long-term gene transcription and expression. Manipulation of temperature (low 36.8°C and high 38.8°C relative to control 37.8 °C) at ...

A common feature of plants being exposed to diverse forms of environmental stress is the increased formation of reactive oxygen species (ROS) in both photosynthesis and respiration. Formation of ROS, however, is not ...

Prediction of soil moisture changes on large scales is of various interests with regard to water resources management. Within this PhD work, different Magnetic Resonance (MR) concepts/apparatus and sequences were applied ...

The aim of the thesis was to test if concentrate supplementation is required in an organic, pasture-based feeding system and if concentrate supplementation influences grazing behavior. The study consisted of two trials, ...