Project 4: Defence and resistance against endophytic pathogens in the brown macroalga Saccharina latissima

In response to recent observations of disease outbreak in seaweed cultivation facilities and wild kelp populations, this area of research is currently exploring the defence and resistance processes of the kelp Saccaharina latissima against pathogens with a focus on brown algal endophytes.

Diseases represent a major threat to cultivated crops. The marine brown macroalga Saccharina latissima (sugar kelp) is the closest Atlantic relative of S. japonica, which dominates the Asian, particularly Chinese, seaweed industry. S. latissima has recently been selected as principal target of brown algal mariculture projects in several European countries. Disease outbreaks have been observed in S. latissima in European seaweed cultivation facilities and wild kelp populations, with unclear etiology. Putative pathogens are endophytic filamentous algae which, according to our unpublished experiments, negatively affect kelp growth, and less well studied fungi, bacteria and viruses. Although certain defence mechanisms of kelp against biotic stress, such as the oxidative burst and some metabolic and transcriptomic regulations, have been identified, the resistance of kelp against pathogens is largely unexplored. Moreover, combined effects of pathogens and other endophytes or symbionts, such as fungi and bacteria, on kelps are entirely unstudied. The brown algal endophytes of the genera Laminariocolax and Laminarionema are highly prevalent in European wild kelp populations. They invade the seaweed stipe and frond, and in some instances can severely perturb morphogenesis.

Miriam Bernard has been appointed researcher for this project at CNRS. Her work will further optimize a kelp pathosystem, based on the re-inoculation of endophytes in lab-reared, fungus-free juvenile Saccharina sporophytes, and implement a quantitative bioassay by monitoring disease symptoms and pathogen colonization. This is necessary in order to establish evidence that the putative pathogen is the causal factor of the disease.

Secondly, Miriam’s research will screen for pathogen-resistant or susceptible kelp sporophytes raised from the existing S. latissima gametophyte collections. It will also compare the phenotypes of resistant and susceptible kelp sporophytes in laboratory-controlled conditions by testing the potential protective effect of fungal endophytes on pathogen/kelp interactions and by studying metabolic regulations of S. latissimi during infection by endophytes. Moreover her work will focus on techniques to isolate and initiate the characterisation of pathogenic organisms causing outbreaks in seaweed farms. Miriam recently completed a secondment at SAMS and she will continue to work on the above techniques with our partners in Brittany (SBR/BR), Ireland (Dommrc) and the Netherlands (NIOZ and Hortimare).