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Title: Differential regulation of duplicate light-dependent protochlorophyllide oxidoreductases in the diatom Phaeodactylum tricornutum

Abstract

Diatoms (Bacilliariophyceae) encode two light-dependent protochlorophyllide oxidoreductases (POR1 and POR2) that catalyze the penultimate step of chlorophyll biosynthesis in the light. Algae live in dynamic environments whose changing light levels induce photoacclimative metabolic shifts, including altered cellular chlorophyll levels. We hypothesized that the two POR proteins may be differentially adaptive under varying light conditions. Using the diatom Phaeodactylum tricornutum as a test system, differences in POR protein abundance and por gene expression were examined when this organism was grown on an alternating light:dark cycles at different irradiances; exposed to continuous light; and challenged by a significant decrease in light availability. As a result, for cultures maintained on a 12h light: 12h dark photoperiod at 200μEm –2 s –1 ( 200L/D), both por genes were up-regulated during the light and down-regulated in the dark, though por1 transcript abundance rose and fell earlier than that of por2. Little concordance occurred between por1 mRNA and POR1 protein abundance. In contrast, por2 mRNA and POR2 protein abundances followed similar diurnal patterns. When 200L/D P. tricornutum cultures were transferred to continuous light ( 200L/L), the diurnal regulatory pattern of por1 mRNA abundance but not of por2 was disrupted, and POR1 but not POR2 protein abundancemore » dropped steeply. Under 1200μEm –2 s –1 ( 1200L/D), both por1 mRNA and POR1 protein abundance displayed diurnal oscillations. A compromised diel por2 mRNA response under 1200L/D did not impact the oscillation in POR2 abundance. When cells grown at 1200L/D were then shifted to 50μEm –2 s –1 (50L/D), por1 and por2 mRNA levels decreased swiftly but briefly upon light reduction. Thereafter, POR1 but not POR2 protein levels rose significantly in response to this light stepdown.« less

Authors:
 [1];  [1];  [1];  [1];  [2]
  1. Univ. of Washington, Seattle, WA (United States)
  2. Stazione Zoologica Anton, Naples (Italy)
Publication Date:
Research Org.:
Texas A & M Univ., College Station, TX (United States)
Sponsoring Org.:
USDOE
OSTI Identifier:
1346608
Alternate Identifier(s):
OSTI ID: 1312900
Grant/Contract Number:
EE0003046
Resource Type:
Journal Article: Published Article
Journal Name:
PLoS ONE
Additional Journal Information:
Journal Volume: 11; Journal Issue: 7; Journal ID: ISSN 1932-6203
Publisher:
Public Library of Science
Country of Publication:
United States
Language:
English
Subject:
60 APPLIED LIFE SCIENCES; chlorophyll; cell cycle and cell division; gene regulation; diatoms; enzyme regulation; algae; messenger RNA; protein abundance

Citation Formats

Hunsperger, Heather M., Ford, Christopher J., Miller, James S., Cattolico, Rose Ann, and Ianora, Adrianna. Differential regulation of duplicate light-dependent protochlorophyllide oxidoreductases in the diatom Phaeodactylum tricornutum. United States: N. p., 2016. Web. doi:10.1371/journal.pone.0158614.
Hunsperger, Heather M., Ford, Christopher J., Miller, James S., Cattolico, Rose Ann, & Ianora, Adrianna. Differential regulation of duplicate light-dependent protochlorophyllide oxidoreductases in the diatom Phaeodactylum tricornutum. United States. doi:10.1371/journal.pone.0158614.
Hunsperger, Heather M., Ford, Christopher J., Miller, James S., Cattolico, Rose Ann, and Ianora, Adrianna. Fri . "Differential regulation of duplicate light-dependent protochlorophyllide oxidoreductases in the diatom Phaeodactylum tricornutum". United States. doi:10.1371/journal.pone.0158614.
@article{osti_1346608,
title = {Differential regulation of duplicate light-dependent protochlorophyllide oxidoreductases in the diatom Phaeodactylum tricornutum},
author = {Hunsperger, Heather M. and Ford, Christopher J. and Miller, James S. and Cattolico, Rose Ann and Ianora, Adrianna},
abstractNote = {Diatoms (Bacilliariophyceae) encode two light-dependent protochlorophyllide oxidoreductases (POR1 and POR2) that catalyze the penultimate step of chlorophyll biosynthesis in the light. Algae live in dynamic environments whose changing light levels induce photoacclimative metabolic shifts, including altered cellular chlorophyll levels. We hypothesized that the two POR proteins may be differentially adaptive under varying light conditions. Using the diatom Phaeodactylum tricornutum as a test system, differences in POR protein abundance and por gene expression were examined when this organism was grown on an alternating light:dark cycles at different irradiances; exposed to continuous light; and challenged by a significant decrease in light availability. As a result, for cultures maintained on a 12h light: 12h dark photoperiod at 200μEm–2 s–1 (200L/D), both por genes were up-regulated during the light and down-regulated in the dark, though por1 transcript abundance rose and fell earlier than that of por2. Little concordance occurred between por1 mRNA and POR1 protein abundance. In contrast, por2 mRNA and POR2 protein abundances followed similar diurnal patterns. When 200L/D P. tricornutum cultures were transferred to continuous light (200L/L), the diurnal regulatory pattern of por1 mRNA abundance but not of por2 was disrupted, and POR1 but not POR2 protein abundance dropped steeply. Under 1200μEm–2 s–1 (1200L/D), both por1 mRNA and POR1 protein abundance displayed diurnal oscillations. A compromised diel por2 mRNA response under 1200L/D did not impact the oscillation in POR2 abundance. When cells grown at 1200L/D were then shifted to 50μEm–2 s–1 (50L/D), por1 and por2 mRNA levels decreased swiftly but briefly upon light reduction. Thereafter, POR1 but not POR2 protein levels rose significantly in response to this light stepdown.},
doi = {10.1371/journal.pone.0158614},
journal = {PLoS ONE},
number = 7,
volume = 11,
place = {United States},
year = {Fri Jul 01 00:00:00 EDT 2016},
month = {Fri Jul 01 00:00:00 EDT 2016}
}

Journal Article:
Free Publicly Available Full Text
Publisher's Version of Record at 10.1371/journal.pone.0158614

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  • Diatoms (Bacilliariophyceae) encode two light-dependent protochlorophyllide oxidoreductases (POR1 and POR2) that catalyze the penultimate step of chlorophyll biosynthesis in the light. Algae live in dynamic environments whose changing light levels induce photoacclimative metabolic shifts, including altered cellular chlorophyll levels. We hypothesized that the two POR proteins may be differentially adaptive under varying light conditions. Using the diatom Phaeodactylum tricornutum as a test system, differences in POR protein abundance and por gene expression were examined when this organism was grown on an alternating light:dark cycles at different irradiances; exposed to continuous light; and challenged by a significant decrease in light availability.more » As a result, for cultures maintained on a 12h light: 12h dark photoperiod at 200μEm –2 s –1 ( 200L/D), both por genes were up-regulated during the light and down-regulated in the dark, though por1 transcript abundance rose and fell earlier than that of por2. Little concordance occurred between por1 mRNA and POR1 protein abundance. In contrast, por2 mRNA and POR2 protein abundances followed similar diurnal patterns. When 200L/D P. tricornutum cultures were transferred to continuous light ( 200L/L), the diurnal regulatory pattern of por1 mRNA abundance but not of por2 was disrupted, and POR1 but not POR2 protein abundance dropped steeply. Under 1200μEm –2 s –1 ( 1200L/D), both por1 mRNA and POR1 protein abundance displayed diurnal oscillations. A compromised diel por2 mRNA response under 1200L/D did not impact the oscillation in POR2 abundance. When cells grown at 1200L/D were then shifted to 50μEm –2 s –1 (50L/D), por1 and por2 mRNA levels decreased swiftly but briefly upon light reduction. Thereafter, POR1 but not POR2 protein levels rose significantly in response to this light stepdown.« less
  • Photosynthetic microbes respond to changing light environments to balance photosynthetic process with light induced damage and photoinhibition. There have been very few characterizations of photosynthetic physiology or biomass partitioning during the day in mass culture. Understanding the constraints on photosynthetic efficiency and biomass accumulation are necessary for engineering superior strains or cultivation methods. We observed the photosynthetic physiology of nutrient replete Phaeodactylum tricornutum growing in light environments that mimic those found in rapidly mixing, outdoor, low biomass photobioreactors. We found little evidence for photoinhibition or non-photochemical quenching in situ, suggesting photosynthesis remains highly efficient throughout the day. Cells doubled theirmore » organic carbon from dawn to dusk and a small percentage – around 20% – of this carbon was allocated to carbohydrates or triacylglycerol. We thus conclude that the self-shading provided by dense culturing of P. tricornutum inhibits the induction of photodamage, and energy dissipation processes that would otherwise lower productivity in an outdoor photobioreactor.« less
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  • Photosynthetic microbes respond to changing light environments to balance photosynthetic process with light induced damage and photoinhibition. There have been very few characterizations of photosynthetic physiology or biomass partitioning during the day in mass culture. Understanding the constraints on photosynthetic efficiency and biomass accumulation are necessary for engineering superior strains or cultivation methods. We observed the photosynthetic physiology of nutrient replete Phaeodactylum tricornutum growing in light environments that mimic those found in rapidly mixing, outdoor, low biomass photobioreactors. We found little evidence for photoinhibition or non-photochemical quenching in situ, suggesting photosynthesis remains highly efficient throughout the day. Cells doubled theirmore » organic carbon from dawn to dusk and a small percentage – around 20% – of this carbon was allocated to carbohydrates or triacylglycerol. We thus conclude that the self-shading provided by dense culturing of P. tricornutum inhibits the induction of photodamage, and energy dissipation processes that would otherwise lower productivity in an outdoor photobioreactor.« less
  • UV radiation is absorbed by PAHs, structurally altering these compounds into a variety of oxygenated products. Until recently, only hazards of parental PAHs in the environment were investigated. This study aims to determine the fate and effects of azaarenes (N-heterocyclic PAHs) together with their photoproducts in marine environments. Photoreaction kinetics of eight asaarenes, ranging from two-ringed to five-ringed structures, were examined using two different light sources: one with an emission peak at 300 nm (UV-B) and the other with an emission peak at 350 nm (UV-A). Azaarenes degraded rapidly in the presence of short-waved light, UV-B being more effective thanmore » UV-A. Especially preexposure of azaarenes to UV-A radiation led to products toxic to the marine diatom Phaeodactylum tricornutum. Since UV-A constitutes a larger fraction of sunlight at the earth surface and in the water column, photolysis by UV-A may increase the toxic risk of aromatic compounds in the marine environment.« less
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