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Phosphorus deficiency alleviates cyanobacterial iron-limitation through a direct PhoB_x0002_ mediated gene regulation

ABSTRACT: Iron (Fe) and phosphorus (P) are essential nutrients with close geochemical association. They exist at low concentrations in surface waters and may be co-limiting resources for phytoplankton growth. However, the adaptive strategies of photosynthetic organisms to Fe/P co-limitation remain largely unknown. Here, we show that phosphorus deficiency increases the growth of Fe-limited cyanobacteria through a PhoB-mediated regulatory network. In addition to its well-recognized role in controlling phosphate homeostasis, PhoB regulates key metabolic processes crucial for Fe-limited cyanobacteria, including ROS detoxification and Fe uptake. Transcript abundances of PhoB-targeted genes are enriched in samples from the P-deplete ocean, and a conserved PhoB binding site is widely present in the promoters of the targets, suggesting that the strategy we discovered may be highly conserved. Our findings provide important molecular insights into the response of cyanobacteria to simultaneous Fe/P nutrient limitation and help in understanding how nutrient availability affects primary productivity in aquatic environments.

ORGANISM(S): Synechocystis sp. PCC 6803

PROVIDER: GSE260812 | GEO | 2024/03/06

REPOSITORIES: GEO

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Project description:Phosphorus (P) is a critical driver of phytoplankton growth and ecosystem structure and function in the ocean. Diatoms are an abundant and widespread functional group of phytoplankton that are responsible for significant amounts of primary production in the ocean, however there has not been a comprehensive study of diatom physiological responses to P deficiency. Here, we coupled deep sequencing of transcript tags and quantitative proteomic analysis from the diatom Thalassiosira pseudonana grown under P-replete and P-deficient conditions. The reads (tags) were mapped to the T. pseudonana genome sequence, confirming expression of 91% of the modeled gene set. A total of 318 genes were differentially regulated with a false discovery rate of p<0.05. A total of 1264 proteins were detected, and of those 136 were differentially expressed with a false discovery rate of p<0.05. Significant changes in the abundance of transcripts and proteins were observed and these changes were coordinated for glycolysis, translation, and multiple biochemical responses to P deficiency. These data demonstrate that diatom P deficiency results in changes in cellular P allocation through polyphosphate production, increased P transport, a switch to utilization of dissolved organic P (DOP) through increased production of alkaline phosphatase metalloenzymes and a diesterase, and a remodeling of the cell surface through production of sulfolipids. Together, these findings reveal that T. pseudonana has evolved a sophisticated response to P deficiency involving multiple biochemical strategies that are likely critical to its ability to rapidly respond to variations in environmental P availability. T. pseudonana (Strain 1335 from the Provosoli-Guillard National Center for the Culture of Marine Phytoplankton (CCMP)) was grown in a modified f/2 medium made from Sargasso Sea water. Macronutrients and vitamin B12, biotin, and thiamine solutions were treated with prepared Chelex-100 resin to remove trace metal contaminants followed by trace-metal clean syringe sterilization to yield final nutrient concentrations of 882 μM NaNO3 and 106 μM Na2SiO3, and vitamin concentrations of 75 pM, 400 pM, and 60 nM, respectively. The Fe concentration was also modified from f/2 to 400 nM. All conditions were run in triplicate at 14 ºC, in constant light (120 µmol photons m-2 s-1). Cells were grown with f/2 phosphorus concentrations (P-replete; 36 µM PO4) and with low phosphorus concentrations (P-deficient; 0.4 µM PO4). Growth was monitored daily with cell counts. Duplicate P-replete treatments were pooled and harvested in mid log phase, and triplicate P-deficient treatments were pooled, and also quickly harvested onto 2 µm filters at the onset of P depletion. All RNA samples were snap frozen in liquid nitrogen. Replicate P-deficient cultures were refed to 36 µM phosphate at the onset of P depletion, and subsequently resumed growth. Additional growth studies were performed as described above substituting glycerolphosphate and adenosine monophosphate at 36 µM, for the phosphate in the medium.

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Phosphorus deficiency alleviates cyanobacterial iron-limitation through a direct PhoB_x0002_ mediated gene regulation

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