Pseudo-nitzschia multistriata is a toxic marine planktonic diatom that blooms regularly in the Mediterranean Sea. The species has a heterothallic mode of reproduction with two distinct mating types. This thesis aimed at exploring the molecular underpinnings of different stages of the sexual reproduction phase in Pseudo-nitzschia multistriata using genomics and transcriptomics approaches. A comparative transcriptomics approach was used to explore the molecular mechanisms involved in the early stages of sexual reproduction in which the opposite mating type strains engage in complex chemical communication and subsequent intracellular signaling. The present thesis identified a number of MT specific genes that are differentially regulated during sexual reproduction. The majority of these MT specific genes could not be annotated using homology based methods, suggesting that they have unique roles in this species. Further, substantial differences between the two mating types were observed in terms of metabolic processes employed during sex. Interestingly, a cell cycle arrest, a phenomenon extensively studied in yeasts, at the onset of the sexual phase was observed in Pseudonitzschia multistriata. Moreover, the genome of Pseudo-nitzschia multistriata along with other four diatom genomes was searched to look for the genes involved in meiosis. Although the majority of meiosis related genes could be identified, a few meiosis specific genes seem to be absent in diatoms, representing a case of lineage specific independent loss, observed in other sexually reproducing species. Lastly, genetic modification methods such as biolistic transformation and chemical mutagenesis were established for gene function studies in this species and the biolistic transformation is already being used to decipher the function of selected sex specific genes identified from RNA-seq experiments.

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The edible red alga Palmaria palmata (dulse) is harvested by hand from the lower intertidal, where it grows on kelp stipes and rocks. It is abundant on rocky shores of Northern Ireland and is so popular when eaten as a dried. product that demand regularly outstrips the supply. Palmaria has been cultivated experimentally by inserting small plants·into ropes, but this is the first determined attempt to cultivate dulse from tetraspores. Mature Palmaria tetrasporophytes are present in winter and release tetraspores under laboratory conditions. Culture string is placed under the mature tetrasporophytes and the released spores settle and attach to the string, and germinate. The aim of this project was to research the requirements for, and offer recommendations about, cultivating Palmaria from spores on a commercial scale. Studies were carried out on wild Palmaria populations with respect to the production of tetraspores, and also to determine the optimum conditions for tetraspore culture in the laboratory and the cultivation of seeded plants in the sea. The following recommendations can be made from this research: • Seeding large amounts of string for a commercial farm will be seasonal as the peak reproductive season for Palmaria is January to April. Stimulation of reproduction by placing plants in short days should be investigated further. • In the laboratory, sporelings are best cultivated in low irradiances (5-10 pmol m-2 S·1) and in high-nutrient media (for example, the culture media F/2). . • Farm costs can be reduced by using less reproductive spore material to seed culture string and keeping sporelings in the laboratory for only 2 weeks before out-planting. them to the sea. • An economically viable seaweed farm can be achieved by removing only the largest plants from culture strings at each harvest and leaving the smaller plants to grow. Strings can then be re-harvested up to four times. • Nets made from culture string should be used instead of individual string lengths (known as droppers). These provide a larger surface area for spores to settle on, and result in less entanglement.

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