Primary metabolism of nematode-induced syncytia

The plant parasitic nematode Heterodera schachtii infects among several crop species also the model plant Arabidopsis thaliana. The parasites induce the formation of specific feeding structures in the plant roots that serve as their sole nutrient source. The required solutes have to be provided by the host plants thus leading to severe damages. Previous studies focussed on the sugar supply of the feeding structures during nematode development. However, incoming solutes may be taken up by the parasites as such or they may be further processed to meet the specific needs of the nematodes and to facilitate the dramatic re-organisation and thus functioning of the syncytia. At present, metabolic processes and pathways in nematode feeding structures are largely unknown. In the present project we plan to analyse products of the primary metabolism of nematode feeding sites by GC-MS. Further, the application of stable isotopes will enable us to follow the dynamics of certain pathways. The information gained in the first part of the project will then be used in the second part. We will choose specific metabolic pathways and enzymatic reactions that showed significant alterations due to nematode infections and study them in detail. Molecular biological techniques such as qRT-PCR and gene silencing as well as enzyme reaction assays and metabolite measurements will be performed. The results of this project will contribute considerably to deepen the understanding of the interaction between cyst nematodes and their hosts. The application of gene silencing and T-DNA insertion mutants will provide information on the function of involved genes and therefore reveal clues for new strategies to develop resistance against cyst nematodes.

Plant-nematode parasitism on cultivated crop species became a big issue in modern agriculture, since these pests cause billions of EUR losses world-wide. The main obstacle in fighting against cyst nematodes is the long-term endurance of the cysts in the soil and their resistance to highly toxic chemicals. Thus, the number of available pest management approaches is limited and development of new strategies is urgently required. Presently, much hope is laid into molecular biological approaches in order to elucidate mechanisms underlying the susceptible host-nematode interaction. Plant breeders use such knowledge in order to produce more tolerant or resistant plant cultivars. The plant parasitic beet cyst nematode Heterodera schachtii induces syncytial feeding structures in Arabidopsis roots. The feeding structures form strong sink tissues that have been suggested to be metabolically highly active. In the present project a metabolic profiling and gene targeted expression analyses were performed in order to study the local and systemic effects of nematode infection on the plant host. The results showed increased levels of many amino acids and phosphorylated metabolites in syncytia, as well as high accumulation of specific sugars such as 1-kestose that do not accumulate naturally in Arabidopsis roots. Further, a C-redistribution study was chosen using 13C-labelled sucrose. The stable isotope was applied onto source leaves and was tracked through shoots, roots, syncytia and eventually the feeding nematodes. With this approach, first, the sink tissues of the pathosystem could be elucidated. Second, the results showed a significant 13C-accumulation in the total non-polar phase, in the non-soluble pellet and in 42 polar metabolites of the analysed chloroform/methanol extracts. The results revealed a specific labelling profile of nematode-induced feeding sites different from all other tissues. They were characterised by high isotope enrichment in specific trisaccharides, amino acids and lipids. In depth analyses studied the roles of the sucrose-cleaving enzymes for the development of H. schachtii. Nematode development was enhanced on multiple INV and SUS mutants. Syncytia of these mutants were characterized by altered enzyme activity and changing sugar pool sizes. Further, the role of arginine cycling during plant-nematode interaction was studied. While silencing of genes involved in arginine synthesis proved beneficial for the nematodes, silencing genes involved in arginine processing had no effect.