Cell walls and symbioses of the economically important brown seaweed Ascophyllum nodosum

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For the last 30 years my research has had a primary focus of the biology of the economically important brown seaweed Ascophyllum nodosum. This alga has unique biological properties: it is both extremely long-lived (potentially 100 years), and has an ecology that makes it a foundation species in the intertidal zone throughout the cold temperate waters of the North Atlantic Ocean. Ascophyllum is the primary host of a complex symbiotic community that includes two obligate red algae (Vertebrata lanosa, Choreocolax polysiphoniae), a systemic obligate fungus (Mycophycias ascophylli), and a facultative epiphytic brown algae (Elachista fucicola) with its associated marine insect (Halocladius variabilis).  My work has largely involved developing an understanding of the symbiotic associations and the ecological roles played by individual components of this community, and the biological processes associated with their interactions and physiological features that allow this community to persist.        Previous ecological work in my laboratory highlighted the need for more fundamental studies in cell biology. This research will make use of techniques successfully used previously, including transmission electron microscopy and confocal microscopy. The work will emphasize the cell biology of brown algal cell walls, and integrate this into a more comprehensive understanding of brown algal cell walls in the context of both pure and applied research. One research component will address whether or not the properties of commercial products derived from the brown alga are indeed based on the brown alga, or whether they are derived from the symbiotic fungus. This will be done by comparing commercial and `home-made' extracts of three related fucoid species of which two species (Ascophyllum and Pelvetia canaliculata) have the same fungal endosymbiont, and one species which does not (Fucus vesiculosus). Several of the symbionts (i.e. Vertebrata, Elachista and Mycophycias) penetrate the host tissue and cause minimal to major damage including localized cell death, and major dissolution of host tissue. These processes will be explored using immunolabelling and electron microscopy to evaluate interactions between species in the context of changing cell wall structure and composition.      Despite its long-lived vegetative thallus, Ascophyllum is continuously breaking down and reforming its cell walls in a process of sloughing and regeneration of the external thallus wall. Annually, this releases about 10% of the standing biomass as detritus. This sloughing process occurs on all vegetative axes and reproductive structures. The chemical triggers that induce sloughing will be a focus of this work. In addition, during maturation of reproductive bodies (i.e. receptacles) Ascophyllum undergoes major wall dissolution. This research will investigate the maturation process by focusing on the cell biology of cell wall breakdown and programmed cell death.