The bacterial-type [4Fe–4S] ferredoxin 7 has a regulatory function under photooxidative stress conditions in the cyanobacterium Synechocystis sp. PCC 6803

Abstract

Ferredoxins function as electron carrier in a wide range of metabolic and regulatory reactions. It is not clear yet, whether the multiplicity of ferredoxin proteins is also reflected in functional multiplicity in photosynthetic organisms. We addressed the biological function of the bacterial-type ferredoxin, Fed7 in the cyanobacterium Synechocystis sp. PCC 6803. The expression of fed7 is induced under low CO₂ conditions and further enhanced by additional high light treatment. These conditions are considered as promoting photooxidative stress, and prompted us to investigate the biological function of Fed7 under these conditions. Loss of Fed7 did not inhibit growth of the mutant strain Δfed7 but significantly modulated photosynthesis parameters when the mutant was grown under low CO₂ and high light conditions. Characteristics of the Δfed7 mutant included elevated chlorophyll and photosystem I levels as well as reduced abundance and activity of photosystem II. Transcriptional profiling of the mutant under low CO₂ conditions demonstrated changes in gene regulation of the carbon concentrating mechanism and photoprotective mechanisms such as the Flv2/4 electron valve, the PSII dimer stabilizing protein Sll0218, and chlorophyll biosynthesis. We conclude that the function of Fed7 is connected to coping with photooxidative stress, possibly by constituting a redox-responsive regulatory element in photoprotection. In photosynthetic eukaryotes domains homologous to Fed7 are exclusively found in chloroplast DnaJ-like proteins that are likely involved in remodeling of regulator protein complexes. It is conceivable that the regulatory function of Fed7 evolved in cyanobacteria and was recruited by Viridiplantae as the controller for the chloroplast DnaJ-like proteins.

Function and Regulation of Ferredoxins in the Cyanobacterium, Synechocystis PCC6803: Recent Advances

“…The four fed mutants, Δ fed4 ::Km r , Δ fed5 ::Km r , Δ fed7 ::Km r and Δ fed9 ::Km r , retained no WT chromosome copies and grew healthily in photoautotrophic conditions. These findings indicate that the fed4 , fed5 , fed7 and fed9 genes are dispensable for Synechocystis growth, in agreement with previous reports on fed4 [ 4 ] and fed7 [ 15 , 18 ]. The complete absence of WT chromosomes in each mutant was also verified in cultures subsequently grown for about 100 generations in the absence of the Km antibiotic to stop counter-selecting the propagation of possibly remaining wild-type (WT) chromosome copies, prior to the PCR assays.…”

“…Our finding is consistent with the occurrence in photosynthetic eukaryotes, such as Chlamydomonas reinhardtii , of a DnaJ-Fed composite protein comprising a DnaJ domain (similar to Sll1384) fused to a Fed domain (similar to Fed7, the closest homolog of this Fed domain in Synechocystis ). Together, these data support the proposal that eukaryotic DnaJ-Fed composite proteins evolved from independent, but physically-interacting DnaJ-like and Fed7-like cyanobacterial proteins [ 15 , 24 ].…”

“…As a step towards the identification of selective functions of Fed7 or Fed9, we noticed that Fed7, but not Fed9, physically interacts with Sll1384, a DnaJ-like protein ( Table 4 ), which is dispensable to cell life [ 23 ], like Fed7 [ 15 , 18 ]. Our finding is consistent with the occurrence in photosynthetic eukaryotes, such as Chlamydomonas reinhardtii , of a DnaJ-Fed composite protein comprising a DnaJ domain (similar to Sll1384) fused to a Fed domain (similar to Fed7, the closest homolog of this Fed domain in Synechocystis ).…”

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

“…Total RNA was isolated from exponentially growing cultures from three independent biological replicates, and RNA concentration and purity were measured as described previously ( Mustila et al 2014 ).…”

Responses to Oxidative and Heavy Metal Stresses in Cyanobacteria: Recent Advances

“…The fed1 , fed2 , fed3 , fed6 and fed8 genes appeared to be essential to the photoautotrophic growth of Synechocystis whereas the fed4 , fed5 , fed7 and fed9 are dispensable [ 10 , 60 , 75 , 76 , 77 ]. Interestingly, the absence of Fed7 or Fed9 (but not Fed4 or Fed5) decrease the tolerance to oxidative (H 2 O 2 ) and metal stresses (Cd for Fed7; and As and U for Fed9 [ 75 ]).…”