Director of Studies: Dr Mahmut Tor, National Pollen and Aerobiology Research Unit, Institute of Science and the Environment, University of Worcester, UK.
Project: “Investigating PAMP/DAMP triggered immunity during Arabidopsis/Hyaloperonospora interactions”.
Everyday plants face with a number of pathogenic and non-pathogenic organisms. In this programme we will investigate the interaction between the Arabidopsis plant and the obligate biotrophic oomycete Hyaloperonospora arabidopsidis.
Oomycetes form a large group of microorganisms that resembles fungi in their morphological features but are more closely related with brown algae. These hemibiotrophic/biotrophic pathogens establish intimate relations with their hosts by forming haustoria during the infection, which are well known structures used for obtaining nutrients from the plant, redirecting host metabolism and suppressing host defence in biotrophy (Hahn and Mendgen, 2001; Voegele and Mendgen, 2003; O’Connell and Panstruga, 2006).
Plants are sessile organisms which, due to their nature, can’t escape pathogens; for this reason they have evolved different mechanisms to cope with those organisms and survive. Plants’ innate immunity is basically a multi-layered recognition system, the first of which involves the recognition of MAMPs (conserved molecules characteristic of an entire class of microbes or PAMPs if the organism is a pathogen) by some surface (transmembrane) receptors, known as pattern recognition receptors (PRRs) (Monaghan and Zipfel, 2012).
FLAGELLIN SENSING2 (FLS2) and EF-TU RECEPTOR (EFR), which specifically bind to flg22 (recognised epitope of flagellin, the major component of bacterial flagellum) and elf18/26 (epitope derived from elongation factor Tu) respectively (Roux et al., 2011) are two intensively studied PRRs In Arabidopsis. After the recognition of these non-self molecules, the plant triggers profound physiological changes, such as bursts of calcium and reactive oxygen species (ROS), ion fluxes, activation of mitogen-associated and calcium-dependent protein kinases (MAPKs and CDPKs) leading to a massive transcriptional reprogramming, known as PTI (PAMPs-triggered immunity) (Monaghan and Zipfel, 2012).
In order to initiate an appropriate defence, some of these PRRs are also able to recognize some molecules that are released or produced under stress conditions, such as infections by pathogenic microorganisms or wound, called damage-associated molecular patterns (DAMPs). In this way the immune response will be amplified (Tör et al, 2009; Roux et al., 2011).
Some specialized pathogenic microbes, however, are able to overcome PTI mechanisms of defence thanks to molecules, called effectors, that can circumvent the detection of PAMPs, or interfere with PTI/MTI by delaying, suppressing or reprogramming host responses. Those effector molecules are products of an avirulence gene that is specific to a certain microbial strain, which could be recognized by a matching R-gene, specific to a certain plant cultivar. After the recognition of the effector by the cognate receptor, effector-triggered immunity (ETI) is initiated with different consequences, first of which is the establishment of a hypersensitive reaction (HR) characterized by local cell death around the infection area (Altenbach and Robatzek, 2007).
The aim of the study is to identify PAMPs from the downy mildew pathogen and DAMPs from the infected Arabidopsis tissues. In addition, we will search for possible receptors in Arabidopsis for these molecules.
Altenbach, D. and Robatzek, S. (2007) Pattern recognition receptors: from the cell surface to intracellular dynamics. Mol Plant Microbe Interact, 20 (9), 1031-1039.
Hahn, M. and Mendgen, K. (2001) Signal and nutrient exchange at biotrophic plant-fungus interfaces. Curr Opin Plant Biol., 4 (4), 322-327.
Monaghan, J. and Zipfel, C. (2012) Plant pattern recognition receptors complexes at the plasma membrane. Curr Opin Plant Biol., 15 (4), 349-357. O’Connell, R.J. and Panstruga, R. (2006) Tête à tête inside a plant cell: establishing compatibility between plants and biotrophic fungi and oomycetes. New Phytologist, 171 (4), 699-718.
Roux, M., Schwessinger, B., Albrecht, C., Chinchilla, D., Jones, A., Holton, N., Malinovsky, F. G., Tör, M., de Vries, S. and Zipfel, C. (2011) The Arabidopsis leucine-rich repeat receptor-like kinases BAK1/SERK3 and BKK1/SERK4 are required for innate immunity to hemibiotrophic and biotrophic pathogens. The Plant Cell, 23, 2440-2455.
Tör, M., Lotze, M. T. and Holton, N. (2009) Receptor mediated signalling in plants: molecular patterns and programmes. Journal of Experimental Botany 60: 3645 – 3654.
Voegele, R. T and Mendgen, K. (2003) Rust haustoria: nutrient uptake and beyond. New Phytologist, 159 (1), 93-100.