Differential cellular responses associated with oxidative stress and cell fate decision under nitrate and phosphate limitations in Thalassiosira pseudonana: Comparative proteomics.

Qun Lin,Qian-Qian Huang,Chris Bowler,Ya-Hui Gao,Xue-Song Li,Chun-Shan Luo,Donald M Anderson,Jun-Rong Liang,Chang-Ping Chen,Adrianna Ianora

doi:10.1371/journal.pone.0184849

Abstract

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.

Highlights

Diatoms are a diverse group of unicellular eukaryotic microalgae that contribute greatly to the global climate, carbon cycling, and ocean ecosystem [1]
Sophisticated, diatom speciesand nutrient stress-specific cellular responses associated with reactive oxygen species (ROS) production and cell death decision were recently identified in response to Fe limitation in T. pseudonana [12,13] and to N limitation in Phaeodactylum tricornutum [3]
When T. pseudonana cells were grown under nitrate-limited (N-limited) condition, there was a significant inhibition of maximum cell abundance, specific growth rate (μ, day−1), and photochemical quantum yield of photosystem II (PS II; Fv/Fm; Fig 1A)

Summary

Introduction

Diatoms are a diverse group of unicellular eukaryotic microalgae that contribute greatly to the global climate, carbon cycling, and ocean ecosystem [1]. They thrive in a wide range of environments [2] and often form massive blooms as a result of their high productivity and efficient turnover rates [3]. Despite their success in marine ecosystems, the metabolic and cellular processes involved in their response to various habitat conditions, especially fluctuations in nutrient levels, remain largely unknown. It is necessary to investigate the biochemical processes that contribute to cell death control, and the mechanisms underlying oxidative stress responses to different stresses, at the system level in diatoms

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