Potato Cyst Nematodes
The potato cyst nematodes (PCN) – Globodera pallida and G. rostochiensis cause damage valued at over £50 million in the UK each year. They are present in two thirds of potato growing fields in the UK and the withdrawal of effective nematicides used by farmers to control PCN means that the future of the crop is threatened for many growers. On a worldwide basis plant parasitic nematodes are thought to cause damage valued at over 100 billion US Dollars each year.
Many plant parasitic nematodes, including PCN, are biotrophic and induce complex feeding structures (syncytia – see picture) in their hosts. The syncytium is a large, multinucleate metabolically active structure and its formation requires massive reprogramming of plant gene expression. Understanding how nematodes induce these structures in plants is an important goal of our work.
Effector biology
Like other biotrophic pathogens, PCN secretes effectors into its host in order to establish infection and to suppress host immunity. We work with other groups in the Dundee Effector Consortium to understand how nematode effectors function in plants. A current focus is how G. pallida effectors suppress host defences and have recently been awarded a joint grant with Leeds University to develop this area. We use a range of techniques including RNAi to understand the functional roles of important nematode proteins in the host-parasite interaction. Cell biology tools are also increasingly important for our work. For example, we have recently shown that some members of a large nematode effector gene family are localised to the nucleus in the plant.
Genomics
Much of our work uses genomics tools. We are partners in a project that is sequencing the genome of the potato cyst nematode Globodera pallida. We have previously undertaken large scale Expressed Sequence Tag analysis of G. pallida and are currently using microarrays and RNAseq to examine changes in gene expression throughout the G. pallida life cycle.
Nematode diversity and avirulence
Resistance genes against biotrophic pathogens operate by detecting pathogen effectors or their activity. Effectors that are recognised in this way are termed Avirulence (Avr) genes. A virulent pathogen does not contain the recognised avirulence gene and is therefore able to overcome a particular resistance source.
Nematode populations display a wide range of virulence against resistance sources. We have a long track record of investigating variation in PCN for diagnostic purposes and in relation to virulence. We are currently using RNAseq and other tools to examine variation in nematode effectors with the aim of identifying avirulence genes from nematodes. A better understanding of nematode avirulence genes offers the prospect of improved resistance breeding tools.
Nematodes and the environment
The development of PCN is influenced by a variety of factors including temperature, resistance of the host and species composition (as G. pallida and G. rostochiensis may be present alone or in mixtures). We are investigating these processes with the aim of providing information that will help improve a model for PCN population dynamics that has been developed in collaboration with the Potato Council. At present it is thought that PCN goes through one generation during each growing season. However, our work has shown that a second generation may occur when temperatures are raised. We are investigating whether potential changes in climate may allow a second generation to occur in the field and the implications of this for management of PCN. We are also exploiting the G. pallida genome sequence to investigate the mechanisms underlying this process.
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