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Abstract

Green macroalgae are widely spread across the coastline of all the continents. Among them, some Ulva species are world renowned for green tides and others grab the interest of the aquaculture production due to fast growth, high nutritive value, bioactive products and bioremediation potential. Ulva spp. have an haplo-diplobiontic sexual life cycle with alternance between sexual and asexual stage. However, data on life cycle dynamics have been limited owing to the difficulties in determining the ploidy or sex using morphological characters of thalli as well as the lack of reliable molecular markers. We used Ulva strains from the 3 main species occurring in Brittany, France, to identify the triggers of reproductive development. To identify the main factors involved in gametogenesis induction, we subjected the seaweeds to several conditions such as thermal shock, various salinities, full moon and various nutrient status, which can stress the algae and activate its gametogenesis. Then we determined morphologically the mating type of the obtained gametes on which we validated the mating type markers. To generate these markers, we used Illumina sequences obtained from a strain collection and we searched for homologous sequences to Ulva partita mating type locus. For the field of algal cultivation, this work will provide tools to isolate and produce axenic strains, to efficiently determine mating type and ploidy and to make controlled crosses and genetic breeding of Ulva spp.