Abstract
Sexual reproduction plays a fundamental role in diatom life cycles. It contributes to increasing genetic diversity through meiotic recombination and also represents the phase where large-sized cells are produced to counteract the cell size reduction process that characterizes these microalgae. With the aim to identify genes linked to the sexual phase of the centric planktonic diatom Skeletonema marinoi, we carried out an RNA-seq experiment comparing the expression level of transcripts in sexualized cells with that of large cells not competent for sex. A set of genes involved in meiosis were found upregulated. Despite the fact that flagellate gametes were observed in the sample, we did not detect the expression of genes involved in the synthesis of flagella that were upregulated during sexual reproduction in another centric diatom. A comparison with the set of genes changing during the first phases of sexual reproduction of the pennate diatom Pseudo-nitzschia multistriata revealed the existence of commonalities, including the strong upregulation of genes with an unknown function that we named Sex Induced Genes (SIG). Our results further broadened the panel of genes that can be used as a marker for sexual reproduction of diatoms, crucial for the interpretation of metatranscriptomic datasets.
Highlights
Sexual reproduction is a ubiquitous event in all eukaryotic lineages, information on the molecular mechanisms at the base of this process are mostly derived from model organisms
In cultures of S. marinoi above the SST transferred to a higher salinity culture medium (Figure 2C), gametangia, i.e., elongated cells with a bent shape which will produce gametes, were observed at 30, 40, and 62 h and swimming gametes were observed after 62 h (Figure 2E)
The same salinity treatment applied to these cells (Figure 2B) did not lead to the appearance of any sexual stage since diatom cells below the SST are incapable of performing sexual reproduction
Summary
Sexual reproduction is a ubiquitous event in all eukaryotic lineages, information on the molecular mechanisms at the base of this process are mostly derived from model organisms. Sexual reproduction plays a fundamental role in diatom life cycles, unicellular microalgae that are important drivers of global biogeochemistry [4]. It is the phase in which genetic recombination occurs when haploid gametes are produced following meiosis, but it represents the phase in which large-sized cells originate. A progressive cell size reduction during mitotic cell division is a distinctive feature of diatom species [5]. This is due to the presence of a rigid siliceous cell wall (the frustule) made of two slightly unequal halves.
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