Angew. Chem. Int. Ed. Engl., published online 12 December 2012; doi:10.1002/anie.201208175

Credit: GEORG POHNERT

Seminavis robusta is a bilaterally symmetric unicellular diatom whose life cycle is characterized by asexual reproduction punctuated by short bursts of sexual reproduction that is used to restore cell size. Cells below a sexual size threshold (SST) of ∼52 mm form MT+ and MT− cells, where MT+ cells are migratory and MT− cells are attractors; both cell types produce mating signals as the process is reciprocal. Gillard et al. took advantage of the migratory behavior of MT+ cells to identify the pheromone produced by MT− cells. The authors visualized by light microscopy the migration of MT+ cells toward beads that were loaded with extracts of MT− cells below the SST and used this system to identify the upregulated pheromone in MT− cell cultures by metabolomics. This approach led to the identification of di-L-prolyl diketopiperazine (diproline) as the MT− pheromone. Diproline production was light dependent, consistent with reports that light triggers mating in pinnate diatoms. Also, diproline was only produced during the mating process, and the attraction assay was only positive when diproline was detectable. Diproline therefore represents one of the pheromones involved in MT−/MT+ mating and most likely binds an as-yet-unidentified receptor on MT+ cells.