Abstract
Programmed cell death (PCD) in marine microalgae was suggested to be one of the mechanisms that facilitates bloom demise, yet its molecular components in phytoplankton are unknown. Phytoplankton are completely lacking any of the canonical components of PCD, such as caspases, but possess metacaspases. Metacaspases were shown to regulate PCD in plants and some protists, but their roles in algae and other organisms are still elusive. Here, we identified and biochemically characterized a type III metacaspase from the model diatom Phaeodactylum tricornutum, termed PtMCA-IIIc. Through expression of recombinant PtMCA-IIIc in E. coli, we revealed that PtMCA-IIIc exhibits a calcium-dependent protease activity, including auto-processing and cleavage after arginine. Similar metacaspase activity was detected in P. tricornutum cell extracts. PtMCA-IIIc overexpressing cells exhibited higher metacaspase activity, while CRISPR/Cas9-mediated knockout cells had decreased metacaspase activity compared to WT cells. Site-directed mutagenesis of cysteines that were predicted to form a disulfide bond decreased recombinant PtMCA-IIIc activity, suggesting its enhancement under oxidizing conditions. One of those cysteines was oxidized, detected in redox proteomics, specifically in response to lethal concentrations of hydrogen peroxide and a diatom derived aldehyde. Phylogenetic analysis revealed that this cysteine-pair is unique and widespread among diatom type III metacaspases. The characterization of a cell death associated protein in diatoms provides insights into the evolutionary origins of PCD and its ecological significance in algal bloom dynamics.
Highlights
Diatoms are an important phytoplankton group that is responsible for about half of marine photosynthesis, playing a significant role in global biogeochemical cycles and in carbon sequestration (Nelson et al, 1995; Rousseaux and Gregg, 2013)
The MC-like protease (MCPs) relative expression levels were very low under various conditions, and the proteins were not detected in previous experiments
The type III MCs, PtMCA-IIIa, PtMCA-IIIb, and PtMCA-IIIc proteins were detected in proteomics datasets (Rosenwasser et al, 2014; Graff van Creveld et al, 2016; Remmers et al, 2018), and had higher gene expression levels in all the examined conditions
Summary
Diatoms are an important phytoplankton group that is responsible for about half of marine photosynthesis, playing a significant role in global biogeochemical cycles and in carbon sequestration (Nelson et al, 1995; Rousseaux and Gregg, 2013). Their evolutionary and ecological success in contemporary oceans suggests that diatoms possess sophisticated mechanisms for. Diverse biotic and abiotic stress conditions can lead to the production of an array of bioactive compounds (infochemicals) that can regulate cell fate and shape population dynamics (Vanelslander et al, 2012; Gillard et al, 2013; Poulson-ellestad et al, 2014; Gallo et al, 2017). The actual redox-sensitive proteins, and the specific oxidation events that regulate cell fate are under-explored in well-established model-systems, and unknown in diatoms
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
