Formation of resting cells is accompanied with enrichment of ferritin in marine diatom Phaeodactylum tricornutum
The formation of resting cells/spores in marine diatoms helps them to survive in environmental changes, whose sedimentation characteristics also drive enhanced carbon fluxes export to the deep ocean. However, the molecular mechanism underlying the transformation remains unclear. Based on the upregulation of ferritin during dormancy in microorganism and its' crucial role in coping with environmental stress, we constructed the ferritin overexpression and silence strains in model marine diatom, Phaeodactylum tricornutum (FTN-OE and FTN Si, respectively). The morphological transformation from fusiform to ovoid were observed among the FTN-OE strains but not the wide type and FTN-Si strains. These FTN-OE oval cells exhibited typical characteristics of resting cells and benthic adaptation, such as lower growth rates, low-light adaptation, silicified valves, the excretion of exopolymeric substances, upregulation of stress-resistant proteins and increased nitrate reserves. Furthermore, FTN-OE oval cells showed increased abscisic acid synthesis and signaling pathways in the transcriptome and proteome . And the abscisic acid signal was detected in FTN-OE oval cells exclusively (2.96 ng g −1 FW), but absent in the FTN Si, FTN-OE fusiform or WT cells. Overall, our results demonstrate that ferritin overexpression in marine diatom have a close relationship with morphological transformation from fusiform to ovoid morphotype , after which they enter a resting stage, which is accompanied by abscisic acid accumulation. This improves our understanding of the molecular processes in diatom resting cells/spores' formation and suggests that ferritin accumulation might improve the sequestration of photosynthetically fixed atmospheric CO 2 into the deep sea.
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