Investigation
of how diatoms cope with the rapid fluctuations in
iron bioavailability in marine environments may facilitate a better
understanding of the mechanisms underlying their ecological success,
in particular their ability to proliferate rapidly during favorable
conditions. In this study, using in vivo biochemical markers and whole-cell
iTRAQ-based proteomics analysis, we explored the cellular responses
associated with reactive oxygen species (ROS) production and cell
fate decision during the early response to Fe limitation in the centric
diatom Thalassiosira pseudonana. Fe limitation caused
a significant decrease in Photosystem (PS) II photosynthetic efficiency,
damage to the photosynthetic electron transport chain in PS I, and
blockage of the respiratory chain in complexes III and IV, which could
all result in excess ROS accumulation. The increase in ROS likely
triggered programmed cell death (PCD) in some of the Fe-limited cells
through synthesis of a series of proteins involved in the delicate
balance between pro-survival and pro-PCD factors. The results provide
molecular-level insights into the major strategies that may be employed
by T. pseudonana in response to Fe-limitation: the
reduction of cell population density through PCD to reduce competition
for available Fe, the reallocation of intracellular nitrogen and Fe
to ensure survival, and an increase in expression of antioxidant and
anti-PCD proteins to cope with stress.
Diatoms are important components of marine ecosystems and contribute greatly to the world’s primary production. Despite their important roles in ecosystems, the molecular basis of how diatoms cope with oxidative stress caused by nutrient fluctuations remains largely unknown. Here, an isobaric tags for relative and absolute quantitation (iTRAQ) proteomic method was coupled with a series of physiological and biochemical techniques to explore oxidative stress- and cell fate decision-related cellular and metabolic responses of the diatom Thalassiosira pseudonana to nitrate (N) and inorganic phosphate (P) stresses. A total of 1151 proteins were detected; 122 and 56 were significantly differentially expressed from control under N- and P-limited conditions, respectively. In N-limited cells, responsive proteins were related to reactive oxygen species (ROS) accumulation, oxidative stress responses and cell death, corresponding to a significant decrease in photosynthetic efficiency, marked intracellular ROS accumulation, and caspase-mediated programmed cell death activation. None of these responses were identified in P-limited cells; however, a significant up-regulation of alkaline phosphatase proteins was observed, which could be the major contributor for P-limited cells to cope with ambient P deficiency. These findings demonstrate that fundamentally different metabolic responses and cellular regulations are employed by the diatom in response to different nutrient stresses and to keep the cells viable.
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