Nitrogen (N) and phosphorus (P) are essential elements whose availability promotes successful growth of phytoplankton and governs aquatic primary productivity. In this study, we investigated the effect of N and/or P deficiency on the sexual reproduction of Prorocentrum cordatum, the dinoflagellate with the haplontic life cycle which causes harmful algal blooms worldwide. In P. cordatum cultures, N and the combined N and P deficiency led to the arrest of the cell cycle in the G0/G1 phases and attenuation of cell culture growth. We observed, that P, but not N deficiency triggered the transition in the life cycle of P. cordatum from vegetative to the sexual stage. This resulted in a sharp increase in percentage of cells with relative nuclear DNA content 2C (zygotes) and the appearance of cells with relative nuclear DNA content 4C (dividing zygotes). Subsequent supplementation with phosphate stimulated meiosis and led to a noticeable increase in the 4C cell number (dividing zygotes). Additionally, we performed transcriptomic data analysis and identified putative phosphate transporters and enzymes involved in the phosphate uptake and regulation of its metabolism by P. cordatum. These include high- and low-affinity inorganic phosphate transporters, atypical alkaline phosphatase, purple acid phosphatases and SPX domain-containing proteins.
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