Welcome to the cell biology world of plant-pathogen interactions!
Most plant pathogens (fungi, oomycetes and bacteria) colonize tissues between cells (Figure 1), and they depend for their development on gaining access to the host cell in order to retrieve nutrients and suppress plant immunity. A paradigm for more than a decade, it has been known that membrane compartments reposition and accumulate at pathogen penetration sites. It is now clear that vesicle secretion and endocytic pathways are engaged by the plant’s immune system to actively defend against potential pathogens. Reciprocally, invasive pathogens have evolved means to utilize these trafficking pathways for the suppression of plant defences and to promote microbial proliferation.
Figure 1: Pathogens invade tissues and cells and reprogram host cell biology (Faulkner and Robatzek, 2012)
At the molecular level, plant immunity in based on the activity of receptors localising at the host plasma membrane (PM) and receptors present in the cytosol. Plasma membrane-localized receptors typically recognize conserved microbial patterns referred to as PAMPs/MAMPs (pathogen-/microbe-associated molecular patterns) and belong to families of receptor-like proteins (RLPs) and receptor-like kinases (RLKs). Perception of PAMPs constitutes an important layer of active plant immunity as these pattern recognition receptors (PRRs) mount defences in response to pathogen molecules prior to cellular invasion.
Figure 2: PRRs are present at distinct membrane compartments within the cell (Beck et al., Curr Opin Plant Biol 2012).
The PRRs for the detection of bacterial flagellin (flg22), EF-Tu (elf18), and chitin are expressed in many cell-types including the highly specialized guard cells forming stomata in the epidermis of plant leaves. Further, at the cellular level, PRRs are present in discrete membrane domains such as the endoplasmatic reticulum (ER) required for quality control of these receptors, the plasma membrane where they can sense their cognate ligands, and in intracellular endosomal vesicles following activation of receptor (Figure 2). Given that a full suite of defence responses requires co-ordination within and between cells and tissues, high-resolution dissection of PRR traffikcing and PAMP-triggered responses will elucidate how plant cells target defence responses in a highly localised and efficient manner. Major open questions in the cell biology of plant-pathogen interactions address the subcellular localisation of PRRs and the intersection with immune responses:
What is the role of PRR subcellular localization for pathogen recognition and defence, and how is PRR subcellular trafficking intersected with the well-described immune responses?
Figure 3: Main questions of PRR trafficking and intersection with flg22 signaling.
We are applying advanced live cell imaging techniques, genetic, biochemical and molecular biological approaches to dissect membrane trafficking and its involvement with plant defence responses at the molecular level. We focus on the induced internalization of the FLS2 receptor recognizing flg22, and on redirected vesicle trafficking in the interaction with pathogens or their secreted effectors. The main objectives of our work are addressing these questions (Figure 3):
What are the trafficking pathways of FLS2, and what are the molecular components regulating FLS2 uptake and sorting? How does FLS2 trafficking intersect with flg22 signalling?
Identifying components controlling the pathogen-triggered membrane trafficking and the intersection with defence signalling will allow understanding of the cellular processes of immunity that will provide robust information to improve food security. Knowledge obtained from this study can be used as strategy for advanced plant breeding, and unravel plant target molecules of pathogen effectors.
Figure 4: Custom algorithms for high throughput imaging in plants.
Recently we have pioneered high content confocal microscopy in plants and developed a series of custom algorithms suited for automated large-scale image analysis. Co-localization studies using established subcellular markers, chemical and genetic inhibition of PRR trafficking revealed exciting new insights into the processes of pathogen-triggered reprogramming of host cell biology, and we believe our current works will elucidate the above raised questions. Other applications of high throughput imaging include the monitoring epidermal cell patterns, plasmodesmata, callose deposition in response to pathogen infection, and closure of stomata (Figure 4), an important level of pre-invasive plant immunity. In this project we address the dynamic response of guard cells to flg22 and dissect the signalling pathways of stomatal closure induced by pathogens in comparison with abiotic stresses (Figure 5). Stomatal behaviors are likely adapting to climate change, so it is therefore important to identify possible consequences of this adaptation for plant immunity.
Figure 5: Questions about pathogen-triggered closure of stomata.
Our research group situated at The Sainsbury Laboratory (www.tsl.ac.uk/) in Norwich, applies a combination of cell biological, genetic, biochemical, and molecular biological approaches to better understand the mechanism of cellular changes in plant-microbe interactions. Our research is supported by the Gatsby Foundation, the European Research Council, the German Research Council, and Industry Funds.
Positions? Interested in joining our forces? If you are seeking for a postdoc, research assistant, PhD or student opportunity, please contact Silke (robatzek@TSL.ac.uk) or our admin team (Kim.Blanchflower@TSL.ac.uk).
Thanks!
