Pierre Cardol Research Associate Belgian funds for research
(F.R.S.-FNRS)
Genetics and Physiology of microalgae
Prof. C. Remacle University of Liège
Botany Institute Belgium
EPC6, London, august 25th 2015, Symbiodinium session
Critical role of oxygen photoreduction
downstream of photosystem I :
photoprotection, energetic adjustment and ROS
production in Symbiodinium
Centre Scientifique de Monaco C. Ferrier-Pagès
E. Béraud
EPC6, London, august 25th 2015, Symbiodinium session
University of Liège S. Roberty (Poster 2 in session 6) Nicolas Berne F. Franck C. Remacle J.C. Plumier B. Bailleul F. Rappaport
G.Finazzi (now CEA grenoble) J. Alric (now CEA cadarache) C. Bowler (ENS, Paris)
Bioenergetics in microalgae
Mitochondrial respiration
CH2O + O2 CO2+ H2O (+ATP)Versus
Chloroplastic photosynthesis
CO2 + H2O + light CH2O + O2 (+ATP) Nucleus Mitochondrion ChloroplastDiversity of photosynthetic microalgae
primary endosymbiosis Heterotroph ancestor Cyanobacteria Photosynthetic ancestor Nucleus Mitochondrion Multiple secondary endosymbiosis Pagotroph ancestor Alveolates Euglenozoa Diatoms Rhizaria HaptophytaSecond
ary Ph
ot
os
yn
th
etic
eu
kary
ot
es
Chlorophyta StreptophytaPrima
ry
Phot
os
yn
the
ti
c
euk
ar
yot
es
RhodophytaAdjustment of photoproduced NADPH/ATP
Electron transport chain : 2 NADPH / 2.6 ATP
CO
2fixation (CBB cycle) : 2 NADPH / 3 ATP
Regulatory mechanisms
-to consume NADPH in excess
-to produce extra ATP
O2 + 4H+ PQ PQH2 2 H20 2 NADPH 8H+ PC thylakoid ATPase 14 H+ 3ADP 3ATP lumen stroma PSII B6f PSI
Linear electron flow : 4é / 2 NADPH / 12 H+
ATP synthase : 14H+ /3 ATP
Alternative electron flows
H2O PQ B PC PSI Fdx NADP+ 6f CBB -CHO PSII O2 FNR PGR NDAPSI-cyclic electron flow
1H
+/e
-1H
+/e
-3H
+/e
-≥3H
+/e
-O2 O2 Chlororespiration -PTOX Mehler reaction O2 Mitochondrial respirationH2O PQ B PC PSI Fdx NADP+ 6f CBB -CHO PSII O2 FNR PGR NDA O2 O2 Chlororespiration -PTOX Mehler reaction O2 Mitochondrial respiration
Alternative electron flows : Biophysical tools
PSI-cyclic electron flow : comparison of PSI and PSII rates
ETRPS = YPS . I . sPS . nPS
Light-dependent oxygen uptake (OUL) : comparison of PSII and O2 exchange rate
ETRPSII = O2 (gross) VO2 = O2 (gross) - OUL
H2O PQ B PC PSI Fdx NADP+ 6f CBB -CHO PSII FNR PGR NDA O2 O2 Mehler reaction O2 Chlororespiration -PTOX Mitochondrial respiration
Diversity of photosynthetic regulations
Ostreococcus sp.
(Prasinophyte, Archaeplastida) (Cardol et al., 2008, PNAS)
Chlamydomonas reinhardtii
(Chlorophyte, Archaeplastida) (Cardol et al., 2003, Plant Physiol.
Cardol et al., 2009, PNAS Dang et al., 2014, Plant Cell)
Phaeodactylum tricornutum
(diatom, stramenopile) (Bailleul et al, 2015, Nature)
PSI-cyclic electron flow
Symbiodinium (Alveolata)
Light-dependent O2 uptake (UOL) capacity up to 45% of ETRPSII
(Jones et al., 1998; Leggat et al., 1999; Badger et al., 2000).
H2O PQ B PC PSI Fdx NADP+ 6f CBB -CHO PSII FNR O2 O2 O2 O2
H2O PQ B PC PSI Fdx NADP+
6f CBB -CHO
PSII FNR
O2
O2 O2
Light-oxygen uptake in Symbiodinium
(Roberty et al., 2014, New Phytol.)HIGH Light
LOW Light
H2O PQ B PC PSI Fdx NADP+
6f CBB -CHO
PSII FNR
O2
O2 O2
Relationship between PSII and PSI
(Roberty et al., 2014, New Phytol.)Chlororespiration -PTOX LOW HIGH Light Light Mitochondrial respiration Photorespiration Calvin Cycle Cyanide + SHAM Glycoladehyde O2 O2
H2O PQ B PC PSI Fdx NADP+
6f CBB -CHO
PSII FNR
O2
Roles of Mehler reaction in Symbiodinium
Light-dependent oxygen uptake Mehler-like reaction
2 e
-+ 2 O
2
2 O
2-(PSI-Fdx)
2 O
2-+
2 H
+
H
2O
2+ O
2(SOD)
H
2O
2+
2ASC
2 H
2O +
2 MDA
(APX)
2 MDA
+ 2e
-+
2H
+
2 ASC
(MDAR)
(Mehler, 1951; Asada et al., 1999)O2
Acts a valve for excess electrons in high light
13
2 H
2O O
2+
4 H
++ 4e
-(PSII)
2 e
-+ 2 O
2
2 O
2-(PSI-Fdx)
Increase of ETR towards O
2(Roberty et al., 2015, Coral Reefs)
Mehler and ROS detoxification capacity
(26°C vs 33°C in High Light)
Imbalance might participate to coral bleaching under
high light and high temperature
Decrease of ROS scavenging capacity
2 O
2-+
2 H
+
H
2
O
2+ O
2(SOD)
H
2O
2+
2ASC
2 H
2O +
2 MDA
(APX)
isolated
Symbiodinium / Stylophora pistillata
14
Does Mehler reaction occur in hospite ?
HIGH Light HIGH Light LOW Light LOW Light
15 PQ B PC PSI Fdx NADP+ 6f CBB -CHO PSII FNR O2 Glycoladehyde Acetazolamide
The main light-dependent oxygen uptake in
isolated Symbiodinium (up to 50% of ETR)
16
H2O PQ B PC PSI Fdx NADP+
6f CBB -CHO
PSII FNR
O2
