The Flavodiiron Protein Flv3 Functions as a Homo-Oligomer During Stress Acclimation and is Distinct from the Flv1/Flv3 Hetero-Oligomer Specific to the O₂Photoreduction Pathway

Abstract

The flavodiiron proteins (FDPs) Flv1 and Flv3 in cyanobacteria function in photoreduction of O2 to H2O, without concomitant formation of reactive oxygen species, known as the Mehler-like reaction. Both Flv1 and Flv3 are essential for growth under fluctuating light (FL) intensities, providing protection for PSI. Here we compared the global transcript profiles of the wild type (WT), Δflv1 and Δflv1/Δflv3 grown under constant light (GL) and FL. In the WT, FL induced the largest down-regulation in transcripts involved in carbon-concentrating mechanisms (CCMs), while those of the nitrogen assimilation pathways increased as compared with GL. Already under GL the Δflv1/Δflv3 double mutant demonstrated a partial down-regulation of transcripts for CCM and nitrogen metabolism, while in FL conditions the transcripts for nitrogen assimilation were strongly down-regulated. Many alterations were specific only for Δflv1/Δflv3, and not detected in Δflv1, suggesting that certain transcripts are affected primarily because of the lack of flv3. By constructing the strains overproducing solely either Flv1 or Flv3, we demonstrate that the homo-oligomers of these proteins also function in acclimation of cells to FL, by catalyzing reactions with as yet unidentified components, while the presence of both Flv1 and Flv3 is a prerequisite for the Mehler-like reaction and thus the electron transfer to O2. Considering the low expression of flv1, it is unlikely that the Flv1 homo-oligomer is present in the WT.

Distinguishing the roles of thylakoid respiratory terminal oxidases in the cyanobacterium Synechocystis sp. PCC 6803

“…Thus, a strong lightinduced oxygen uptake component observed in the wild type was missing in the Δflv1/3 mutant. This was in line with previous reports, demonstrating that oxygen uptake in wild-type Synechocystis was strongly stimulated in the light due to Flv1/3 activity occurring downstream of PSI (Helman et al, 2003(Helman et al, , 2005Allahverdiyeva et al, 2011, Mustila et al, 2016.…”

“…3). This is yet another demonstration of Cyd-driven light-induced oxygen uptake when cells are grown under suboptimal conditions, despite the absence of changes in cyd transcript level under FL (Mustila et al, 2016).…”

Flavodiiron Proteins Promote Fast and Transient O2 Photoreduction in Chlamydomonas

“…Based on O 2 photoreduction measurements in Δflv1 and Δflv3 cyanobacterial mutants, it was concluded that Flv3 function as a hetero-dimer with Flv1 (Helman et al, 2003;Allahverdiyeva et al, 2011). However, a functional Flv3 homo-oligomer may also be formed, as deduced from the overproduction of Flv3 in Synechocystis (Mustila et al, 2016). On the other hand, Flv2 and Flv4 protect PSII by a different mechanism and using a yetuncharacterized electron acceptor (Zhang et al, 2012;Bersanini et al, 2014).…”

A new approach for sustained and efficient H2 photoproduction by Chlamydomonas reinhardtii

“…The gas exchange was measured by membrane inlet mass spectrometry (MIMS) using a modified DW1 (Hansatech Instruments) electrode chamber as previously described. 19 The long-term H 2 photoproduction experiments were performed with a 10 mL cell suspension in 70 mL gas-tight vials under an Ar atmosphere. The pulses of white light (280 mmol photons m À2 s À1 ) interrupted by dark periods or the constant light of the same intensity were provided by the growth chamber (AlgaeTron AG 130-ECO, PSI).…”