Light intensity and spectral composition drive reproductive success in the marine benthic diatom Seminavis robusta

Abstract

The properties of incident light play a crucial role in the mating process of diatoms, a group of ecologically important microalgae. While species-specific requirements for light intensity and photoperiod have been observed in several diatom species, little is known about the light spectrum that allows sexual reproduction. Here, we study the effects of spectral properties and light intensity on the initiation and progression of sexual reproduction in the model benthic diatom Seminavis robusta. We found that distinct stages of the mating process have different requirements for light. Vigorous mating pair formation occurred under a broad range of light intensities, ranging from 10 to 81 µE m−2 s−1, while gametogenesis and subsequent stages were strongly affected by moderate light intensities of 27 µE m−2 s−1 and up. In addition, light of blue or blue–green wavelengths was required for the formation of mating pairs. Combining flow cytometric analysis with expression profiling of the diatom-specific cyclin dsCyc2 suggests that progression through a blue light-dependent checkpoint in the G1 cell cycle phase is essential for induction of sexual reproduction. Taken together, we expand the current model of mating in benthic pennate diatoms, which relies on the interplay between light, cell cycle and sex pheromone signaling.

Potential for the Production of Carotenoids of Interest in the Polar Diatom Fragilariopsis cylindrus

“…When using equivalent PURs between light treatments, a slower growth rate, due to a higher quantum requirement, is to be expected under monochromatic red light in diatoms [ 38 , 64 , 71 , 72 ]. The dramatically slower growth rate (close to 0 day −1 ) was similar to previous reports in temperate planktonic and benthic strains [ 66 ]. Nevertheless, apart from this observation and similar cell Chl a content with ‘white’ and blue lights, the response of F. cylindrus to red light appeared stronger than in temperate strains [ 38 , 64 ].…”

“…The 7 °C growth rate was nearly doubled under blue compared to ‘white’ light, with no differences in photosynthesis and photoprotection, a feature also observed at 0 °C (11.7 µmol photons m −2 s −1 PUR) but to a lower extent. This observation was also reported in temperate counterparts, and shown to be based on the cell cycle and sexual reproduction [ 66 , 70 ] and/or on improved energy vs. biomass allocation [ 38 , 39 , 63 ].…”

“…Interestingly, when comparing blue and ‘white’ light treatments of the same PUR (5.8 and 11.7 µmol photons m −2 s −1 PUR), we did not observe (apart from a consistent but not significant increase in NPQ) the blue light-triggered high-light acclimation previously described in temperate diatoms [ 38 , 63 ] and shown to be controlled by the aureochrome blue light photoreceptor family [ 64 , 65 ], although F. cylindrus does possess aureochromes [ 66 ]. F. cylindrus is usually found to be abundant at the sea-ice bottom horizon and underneath ice [ 51 , 53 ] where blue wavelengths dominate [ 43 , 44 ].…”

The Molecular Life of Diatoms

“…Sexual reproduction does not occur in the dark in Haslea ostrearia and S. robusta, in the latter species potentially through inhibition of sex pheromone biosynthesis (Mouget et al 2009;Gillard et al 2013). Gametogenesis was maximal at a photon flux density of 96 μE m À2 s À1 in Nitzschia lanceolata, but the highest level of auxosporulation in H. ostrearia and S. robusta was observed at intensities below 40 and 27 μE m À2 s À1 respectively (Davidovich 1998;Mouget et al 2009;Bilcke et al 2021b). In addition, sexual reproduction was highly dependent on the presence of red light in H. ostrearia and blue light in S. robusta (Mouget et al 2009;Bilcke et al 2021b).…”

“…Gametogenesis was maximal at a photon flux density of 96 μE m À2 s À1 in Nitzschia lanceolata, but the highest level of auxosporulation in H. ostrearia and S. robusta was observed at intensities below 40 and 27 μE m À2 s À1 respectively (Davidovich 1998;Mouget et al 2009;Bilcke et al 2021b). In addition, sexual reproduction was highly dependent on the presence of red light in H. ostrearia and blue light in S. robusta (Mouget et al 2009;Bilcke et al 2021b). Finally, the physiological state of many pennate diatoms needs to be excellent before cells can become sexualized (Amato 2010).…”