Characterisation of the processes of nutrient flow from a host plant to a parasitic nematode

Cyst nematodes are small with a length of only 0.5mm but there can be thousands of millions in one hectare of field soil. Each nematodes moves from the soil into the roots of its host crop plant. Once inside the plant it loses the ability to move and feeds at just one place. Approximately 75 % of the nematode population becomes female. Females feed for about 8 weeks growing to about 1000 times their original size and laying up to 700 eggs. They modify one plant cell. This provides all the nematode's food for several weeks. This cell is highly specialised structure and transport nutrients from the plant flow though this cell to the feeding nematode. We have identified the plant molecules that transport the essential nutrients the feeding nematode needs. This project will define how these molecules are distributed around the specialsed plant cell that gathers nutrients to supply to the nematode parasite. We will determine how the walls of this cell are changed to allow it to merge with other cells, grow in size and also support the flow of nutrients through it to the feeding nematode. We will use antibodies designed to recognise components of the cell wall to understand the structure of the wall of this cell. The nematode must ensure its feeding does not kill the plant cell from which it feeds. If that happened the nematode would die. The nematode makes a feeding tube that has holes all the way along its length, not just at the end. We will find out if this allows the nematode to feed by without damaging the internal structure of the plant cell. If the nematode took the contents of the cell through just a single hole in the feeding tube (like a straw) the cell might be badly damaged. We want to understand how these plant parasites feed from plant cells. No other animals feed in this way. Nematodes damage many crop plants throughout the world. Cyst nematodes cause losses of approximately £43 million each year just to UK potato crops. This new knowledge may help to find a way to stop the nematodes from feeding. This would protect plants from the damage they cause. Currently farmers often use pesticides that harm the environment and can damage the health of farm workers. We have shown before that new knowledge can help develop better ways of controlling nematodes in the future.

Cyst nematodes invade plant roots from soil and become obligate endoparasites. A single plant cell is selected by each nematode. It undergoes cellular redevelopment and forms a syncytium with other adjacent cells. The female nematode feeds exclusively from this single syncytium throughout its development. They feed for approximately 8 weeks growing to c.100x their original size and draining the plant of vital resources when many establish concurrently on a root system. This work characterises three important and inter-related aspects of this unique host/pathogen interaction that characterise nutrient flow from the plant to the parasite: 1) the distribution of transporter proteins in the plasma membrane of the syncytium and their role in replacing the nutrients withdrawn from the cell by the nematode, 2) the change in plant cell architecture that accommodates the effective functioning of these cells and 3) the ability of the nematode to feed continually without lethal consequences for the cell. We have carried out microarray analysis using syncytial material within c. 2 mm root lengths thereby minimising dilution of that mRNA originating from the syncytium. This has allowed us to identify a number of transporter proteins that are up regulated in the infected sample. In this project we will determine the pattern of expression of these transporters in the syncytium. We will make translation fusions of these proteins with Green Fluorescent Protein and use confocal imaging to determine their distribution around the plasma membrane of the syncytium. It is highly likely that there will be a greater concentration of these transporters where cell wall invaginations provide an enhanced surface area in contact with the vasculature. The cell wall of the syncytium is altered in ways that presumably favour syncytial expansion and high nutrient influx. We will use antibodies designed to recognise components of the cell wall to understand the structure of the wall around the circumference of the syncytium. We have observed carbohydrate moieties of the syncytial wall in preliminary work and gained evidence that its carbohydrate components are significantly different from those of other plant cell walls. The nematode makes a feeding tube, a unique structure within the syncytium. Our work to-date suggests that feeding tubes are ultrafilters. We propose to study if their role is to ensure continual uptake of permeate is achieved without perturbing the internal structure of the cell. We seek to define why each feeding tube has a functional life of only a few hours. Commercially produced ultrafiltration devices provide a preliminary understanding of the problems associated with their use, such as blocking and gel formation on the outer surface. The attributes of the nematode feeding tube will be analysed and used to determine the biological role of this unique structure.