How does a plant pathogen hijack its host's secretory pathway?

Background. Plant-parasitic nematodes are important agricultural pests that have complex interactions with their host. The most damaging species secrete effector proteins into their host roots to induce and maintain unique structures, termed feeding-sites. A striking feature of the affected root cells is proliferated cytoplasm enriched in organelles, formed at the expense of the central vacuole. Our core hypothesis is that nematodes can use effectors to re-programme membrane trafficking of plant cells to achieve this fundamental remodelling whilst also exploiting the secretory pathway to exert effector function.

Objectives.
1. Characterise the early changes to secretory pathway organelles that occur in plant parasitic nematode feeding sites.
2. Investigate the role of nematode effectors in influencing secretion, ER retention and vacuolar transport.
3. Elucidate the pathways by which nematode effectors introduced into the host cytoplasm are delivered to the apoplast.

Novelty. The mechanism driving the cytological changes that occur in nematode feeding sites, and the specific effectors involved, are currently unknown. The work will also provide new insights into protein trafficking pathways in plants.

Timeliness. The project is facilitated by tools recently developed by the Denecke Group, such as the full portfolio of vacuolar and endosomal markers and secretory cargo protoplast assays.

Experimental Approach. Double-fluorescent reporter lines of Arabidopsis with different secretory pathway organelles marked will be infected with nematodes. Confocal microscopy will be used to examine subcellular changes taking place during the early stages of feeding site formation. A range of nematode effectors will be expressed in secretory cargo protoplast assays to identify those that influence vacuolar and/or ER function. Yeast-2-hybrid analysis will identify plant interacting partners for effectors of interest - confirmed by coimmunoprecipitation. Protoplast secretion assays using native and mutant effectors will define the export pathway of nematode effectors that function in the apoplast despite being delivered into the cytoplasm.

The project is built on the hypothesis that plant parasitic nematodes can re-programme embrane trafficking of host plant cells so that the normal route to maintain the central vacuole is eliminated to enable expansion of the plasma membrane and the ribosome rich cytosol. The student will test this hypothesis and establish if the secreted protein effectors produced by the nematode are responsible for the fundamental reprogramming of the plant secretory pathway. By dissecting the mechanisms involved in this parasitic interaction, the project will shed new light on a key aspect of plant cell biology.