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Target Concepts:
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Query: UMLS:C0003129 (
Anoxia
)
551
document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)
While photosynthetic linear electron flow produces both ATP and NADPH, cyclic electron flow (CEF) around photosystem I (PSI) and cytochrome b6f generates only ATP. CEF is thus essential to balance the supply of ATP and NADPH for carbon fixation; however, it remains unclear how the system tunes the relative levels of linear and cyclic flow. Here, we show that PETO, a transmembrane thylakoid phosphoprotein specific of green algae, contributes to the stimulation of CEF when cells are placed in anoxia. In oxic conditions, PETO co-fractionates with other thylakoid proteins involved in CEF (ANR1, PGRL1, FNR). In PETO-knockdown strains, interactions between these CEF proteins are affected.
Anoxia
triggers a reorganization of the membrane, so that a subpopulation of PSI and cytochrome b6f now co-fractionates with the CEF effectors in sucrose gradients. The absence of PETO impairs this reorganization. Affinity purification identifies ANR1 as a major interactant of PETO. ANR1 contains two ANR domains, which are also found in the N-terminal region of NdhS, the
ferredoxin
-binding subunit of the plant
ferredoxin
-plastoquinone oxidoreductase (NDH). We propose that the ANR domain was co-opted by two unrelated CEF systems (PGR and NDH), possibly as a sensor of the redox state of the membrane.
...
PMID:PETO Interacts with Other Effectors of Cyclic Electron Flow in Chlamydomonas. 2676 21
Ferredoxins (FDX) and the FDX:NADP
+
oxidoreductase (FNR) represent a key junction of electron transport downstream of photosystem I (PSI). Dynamic recruitment of FNR to the thylakoid membrane has been considered as a potential mechanism to define the fate of photosynthetically derived electrons. In this study, we investigated the functional importance of the association of FNR with the photosynthetic apparatus in Chlamydomonas reinhardtii. In vitro assays based on NADP
+
photoreduction measurements as well as NMR chemical shift perturbation analyses showed that FNR preferentially interacts with
FDX1
compared to
FDX2
. Notably, binding of FNR to a PSI supercomplex further enhanced this preference for
FDX1
over
FDX2
, suggesting that FNR is potentially capable of channelling electrons towards distinct routes. NADP
+
photoreduction assays and immunoblotting revealed that the association of FNR with the thylakoid membrane including the PSI supercomplex is impaired in the absence of Proton Gradient Regulation 5 (PGR5) and/or Proton Gradient Regulation 5-Like photosynthetic phenotype 1 (PGRL1), implying that both proteins, directly or indirectly, contribute to the recruitment of FNR to the thylakoid membrane. As assessed via in vivo absorption spectroscopy and immunoblotting, PSI was the primary target of photodamage in response to high-light stress in the absence of PGR5 and/or PGRL1.
Anoxia
preserved the activity of PSI, pointing to enhanced electron donation to O
2
as the source of the observed PSI inactivation and degradation. These findings establish another perspective on PGR5/PGRL1 knockout-related phenotypes and potentially interconnect FNR with the regulation of photosynthetic electron transport and PSI photoprotection in C. reinhardtii.
...
PMID:Association of Ferredoxin:NADP
+
oxidoreductase with the photosynthetic apparatus modulates electron transfer in Chlamydomonas reinhardtii. 2859 95
