GENOmics of Marine Algae and their Pathogens: a transcriptomic picture of pathogenicity, disease and resistance using the Ectocarpus-Eurychasma model

DO ALGAE EVER GET SICK, AND WHY DOES IT MATTER?
Brown algae make up over 70% of the biomass of our rocky seashores. As the seaweed aquaculture industry grows exponentially worldwide, their economic importance is increasing rapidly. In the UK and other Western countries, algae are being considered as a potential sustainable biofuel source. The development of experimental aquaculture facilities is currently attracting considerable investment in the context of the ongoing transition towards a low carbon economy.
Like any other living organism, brown algae are plagued by diseases caused by fungi, bacteria or viruses. Among them, Eurychasma dicksonii - the parasite that I am studying - is very common and widespread. However, very little is known about its biology, or indeed the biology of similar algal pathogens. This lack of information hampers our capacity to comprehend the impact of diseases in natural algal populations, and more broadly, on marine ecosystem functioning. Additionally, the interplay between natural populations, crops and their pathogens, which are central to the design of management policies concerning any agricultural production, remain entirely unknown for marine seaweeds.
For these reasons, I have developed a laboratory model between Eurychasma and the filamentous brown alga Ectocarpus siliculosus, which I suggest to use in GenoMAP to help tackle these questions.

PATHOGENICITY AND IMMUNITY, THE YIN AND YANG OF DISEASE
In GenoMAP, I propose to apply cutting-edge genomics techniques to identify the gene repertoire of Eurychasma and elucidate the molecular basis of its pathogenicity. Since Eurychasma is also related to many other pathogens that have a devastating effect in agriculture (e.g. potato blight, grape mildew), aquaculture (fish saprolegniosis, crayfish plague), and on natural populations (sudden oak death), a cross-species comparative genomic analysis will have wide-ranging implications for understanding the biology and evolution of this group of pathogens (so-called oomycetes).
Secondly, I propose to conduct a large scale transcriptomic experiment to follow the expression of Ectocarpus and Eurychasma genes in infected disease-susceptible and disease resistant algal strains. This will give us information on the molecular basis of disease resistance in the brown alga Ectocarpus, whilst also shedding light on the strategies used by Eurychasma to defeat the immune system of its host. Indeed, and although not always successful, algae actually do have an immune system and try to defend themselves against pathogens. My results so far show that some of them indeed resist Eurychasma infection attempts by inducing the early death of infected cells, which prevents reproduction of the pathogen and subsequently, the spread of infection.
Finally, this dataset will provide a first insight on the natural variation between disease-susceptible and disease-resistant algal strains. In particular, In particular, I will investigate the variation in the so-called LRR-ROCO and NB-ARC-TPR gene families. Both display striking structural and evolutionary features that make them excellent candidates for being involved in pathogen perception.

Overall, GenoMAP will help us understand some of the fundamental biological mechanisms underpinning algal-host pathogen interactions. In the future, this new knowledge will be invaluable to address ecologically-relevant questions from a position of strength and novelty. Thus, in conjunction with ongoing parallel work, GenoMAP will go one step further towards the development of new evidence-based concepts on the fundamental - yet largely overlooked - impact of eukaryotic algal pathogens in marine ecosystems.

Besides the academic beneficiaries detailed elsewhere, other groups will benefit from the research undertaken in GenoMAP.

1) The most important long term beneficiaries are government bodies and policy makers, in charge of designing science-informed environmental management policies. Scottish and UK laws are currently being reviewed to cover seaweed aquaculture activities. New policies will need to take into account the environmental impact of these new activities on natural algal populations and marine ecosystems as a whole.

2) The Asiatic seaweed aquaculture sector, which has undergone a drastic transition towards intensive production over the last few decades, is an eloquent example of forthcoming difficulties for Western countries: whilst mostly regarded as anecdotal in the past, diseases are now responsible of large-scale epidemic outbreaks in seaweed farms, cause massive economic loss, with hardly any control method in place. GenoMAP will develop the national capacity to support the nascent UK seaweed culturing industry, by creating relevant expertise and anticipating forthcoming difficulties. This aspect directly addresses NERC's mission to deliver a highly-skilled workforce and generate transferrable skills for the UK economy.

3). We think that NERC will also benefit from GenoMAP. The recent NERC NEOMICS consultation has clearly spelled out the need for NERC to develop a coordinated genomics strategy and build up its capacity in order to deliver world-class leadership (NEOMICS report, Oct 2010). In parallel, the NERC Oceans 2025 Advisory Board recently identified marine genomics as an area the potential of which should be better addressed, in the view of its relevance to NERC's missions and priority areas (O2025 PAB recommendations, May 2010).

GenoMAP's comprehensive impact plan has been designed to efficiently disseminate the results of the project to academics, end users and the general public through a diversity of complementary undertakings, and with the support of communication professionals.