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Abstract:
Finding a mate: Diatoms use chemical signals to sense the presence of and find their mating partners. When the metabolic profiles of sexually active and inactive cells were compared, a highly up‐regulated metabolite generated in the attracting mating type was identified as di‐L‐prolyl diketopiperazine, the first diatom pheromone.
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Diatoms are unicellular photosynthetic organisms that often dominate primary production in pelagic and benthic aquatic ecosystems.1, 2 Despite their central role in the biosphere, little is known about their pheromone chemistry and their lifecycle, which is characterized by asexual population growth alternating with short bursts of sexual reproduction.3, 4 Diatoms are unique among microalgae in that sexual reproduction is only possible below a species‐specific sexual size threshold (SST).5 This SST is intimately linked to the characteristic cell division of diatoms. Due to their rigid biomineralized cell wall, mitotic division results in a reduction in size (Figure 1).6 Size is restored typically by sexual reproduction. Upon germination, a zygote generates a large initial cell, which begins a new round of vegetative proliferation.6, 7 In the ancestral group of predominantly planktonic centric diatoms, environmental cues induce meiosis in cells below the SST, resulting in the formation of eggs and flagellated sperm.8 However, in the youngest and most species‐rich pennate raphid diatoms,9 which have adopted a primarily benthic lifestyle, it is the pairing of diploid cells that triggers the production of isogametes.6 Although the SST is known to control the mating capacity of pennate diatoms and indirect evidence suggests the involvement of pheromones, the regulatory principles underlying the differentiation of mating cells and the identity of the pheromones remain unknown.
