PhD Research Student
The oomycetes include a unique group of biotrophic and hemibiotrophic plant pathogens including Plasmapora viticola (grapevine downy mildew), Albugo candida (white rust), Bremia lactucae (lettuce downy mildew), Hyaloperonospora arabidopsidis (downy mildew on Arabidopsis) and Phytophthora infestans (potato and tomato late blight; Kamoun 2003; Hardham 2007). These 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 inbiotrophy (Hahn and Mendgen, 2001; Voegele and Mendgen, 2003; O’Connell and Panstruga, 2006). B. lactucae, P. viticola or P. infestans have a significant economic importance in agriculture. H. arabidopsidis in Arabidopsis thaliana has been developed as an important model system to study plant-microbe interactions.
In addition, A. candida provides an alternative model on Arabidopsis, however, it has not been fully explored despite interesting characteristics such as the suppression of R-gene mediated and non-host resistance mechanisms to allow the growth of a second parasite like H. arabidopsis and causing a hormonal imbalance, which induces “green island” formation (Cooper et al., 2002).
Understanding the mechanisms of microbial pathogenesis and plant-microbe interactions has motivated plant pathologists for a long while. In nature, plants are generally resistant to most pathogens due to their innate ability to recognize pathogen derived molecules and to mount a series of carefully orchestrated and highly evolved defence responses. In the last few years, significant progress has been made in the understanding of interactions between eukaryotic pathogens, including oomycetes, ascomycetes and basidiomycetes, and their host plants (Allen et al., 2004; Catanzariti et al., 2006; Shen et al., 2007b). Results from these studies led to the establishment of a general consensus on plant-microbe interactions, which is that; a) pathogens have pathogen associated molecular pattern molecules (PAMPs) and effector molecules that modulate the immune system (Kamoun, 2006; Lotze et al., 2007); b) the plant innate immune system is a collection of subsystems that carry out distinct functions in the host’s defence; c) the cell surface receptors or pattern recognition receptors (PRR) and cytoplasmic receptors or nucleotide binding site-leucine rich repeat (NB-LRR) proteins play a significant role in the detection of these PAMPs and effectors (Chisholm et al. 2006), and d) effector molecules are virulence factors and have the ability to suppress the immune system ofthe plant (Bos et al., 2006; Jones and Dangl 2006).
Recent genomic studies on the oomycete pathogens including P. sojae, P. ramorum, P. infestans and H. arabidopsidis (Win et al., 2007; Whisson et al., 2007) have revealed hundreds of hypothetical effectors that are secreted into the apoplast or the cytoplasm of the host plants.
In the proposed research, we aim to understand the role of apoplastic virulence factors form H. arabidopsidis in immune activation. Using bioinformatics, molecular biology and proteomics, we want to identify effectors delivered to apoplast, express them in vitro and determine if any of them are recognized by cell surface receptors.
Director of Studies: Dr Mahmut Tor, National Pollen and Aerobiology Research Unit, Institute of Science and the Environment, University of Worcester, UK.
Dr Lee Byrne, Institute of Science and the Environment, University of Worcester, UK,
Prof Roy Kennedy, National Pollen and Aerobiology Research Unit.