The C-terminus of a diatom plant-like cryptochrome influences the FAD redox state and binding of interaction partners

One More for Light-triggered Conformational Changes in Cryptochromes: CryP from Phaeodactylum tricornutum

Cryptochromes are a ubiquitously occurring class of photoreceptors. Together with photolyases, they form the Photolyase Cryptochrome Superfamily (PCSf) by sharing a common protein architecture and binding mode of the FAD chromophore. Despite these similarities, PCSf members exert different functions. Photolyases repair UV-induced DNA damage by photocatalytically driven electron transfer between FADH¯ and the DNA lesion, whereas cryptochromes are light-dependent signaling molecules and trigger various biological processes by photoconversion of their FAD redox and charge states. Given that most cryptochromes possess a C-terminal extension (CTE) of varying length, the functions of their CTE have not yet been fully elucidated and are hence highly debated. In this study, the role of the CTE was investigated for a novel subclass of the PCSf, the CryP-like cryptochromes, by hydrogen/deuterium exchange and mass-spectrometric analysis. Striking differences in the relative deuterium uptake were observed in different redox states of CryP from the diatom Phaeodactylum tricornutum. Based on these measurements we propose a model for light-triggered conformational changes in CryP-like cryptochromes that differs from other known cryptochrome families like the insect or plant cryptochromes.

Cryptochrome PtCPF1 regulates high temperature acclimation of marine diatoms through coordination of iron and phosphorus uptake

Increasing ocean temperatures threaten the productivity and species composition of marine diatoms. High temperature response and regulation are important for the acclimation of marine diatoms to such environments. However, the molecular mechanisms behind their acclimation to high temperature are still largely unknown. In this study, the abundance of PtCPF1 homologs (a member of the cryptochrome-photolyase family in the model diatom Phaeodactylum tricornutum) transcripts in marine phytoplankton is shown to increase with rising temperature based on Tara Oceans datasets. Moreover, the expression of PtCPF1 in P. tricornutum at high temperature (26 °C) was much higher than that at optimum temperature (20 °C). Deletion of PtCPF1 in P. tricornutum disrupted the expression of genes encoding two phytotransferrins (ISIP2A and ISIP1) and two Na+/P co-transporters (PHATRDRAFT_47667 and PHATRDRAFT_40433) at 26 °C. This further impacted the uptake of Fe and P, and eventually caused the arrest of cell division. Gene expression, Fe and P uptake, and cell division were restored by rescue with the native PtCPF1 gene. Furthermore, PtCPF1 interacts with two putative transcription factors (BolA and TF IIA) that potentially regulate the expression of genes encoding phytotransferrins and Na+/P co-transporters. To the best of our knowledge, this is the first study to reveal PtCPF1 as an essential regulator in the acclimation of marine diatoms to high temperature through the coordination of Fe and P uptake. Therefore, these findings help elucidate how marine diatoms acclimate to high temperature.