PT  - JOURNAL ARTICLE
AU  - Bersanini, Luca
AU  - Battchikova, Natalia
AU  - Jokel, Martina
AU  - Rehman, Ateeq
AU  - Vass, Imre
AU  - Allahverdiyeva, Yagut
AU  - Aro, Eva-Mari
TI  - Flavodiiron Protein Flv2/Flv4-Related Photoprotective Mechanism Dissipates Excitation Pressure of PSII in Cooperation with Phycobilisomes in Cyanobacteria
AID  - 10.1104/pp.113.231969
DP  - 2014 Feb 01
TA  - Plant Physiology
PG  - 805--818
VI  - 164
IP  - 2
4099  - http://www.plantphysiol.org/content/164/2/805.short
4100  - http://www.plantphysiol.org/content/164/2/805.full
SO  - Plant Physiol.2014 Feb 01; 164
AB  - Oxygenic photosynthesis evolved with cyanobacteria, the ancestors of plant chloroplasts. The highly oxidizing chemistry of water splitting required concomitant evolution of efficient photoprotection mechanisms to safeguard the photosynthetic machinery. The role of flavodiiron proteins (FDPs), originally called A-type flavoproteins or Flvs, in this context has only recently been appreciated. Cyanobacterial FDPs constitute a specific protein group that evolved to protect oxygenic photosynthesis. There are four FDPs in Synechocystis sp. PCC 6803 (Flv1 to Flv4). Two of them, Flv2 and Flv4, are encoded by an operon together with a Sll0218 protein. Their expression, tightly regulated by CO2 levels, is also influenced by changes in light intensity. Here we describe the overexpression of the flv4-2 operon in Synechocystis sp. PCC 6803 and demonstrate that it results in improved photochemistry of PSII. The flv4-2/OE mutant is more resistant to photoinhibition of PSII and exhibits a more oxidized state of the plastoquinone pool and reduced production of singlet oxygen compared with control strains. Results of biophysical measurements indicate that the flv4-2 operon functions in an alternative electron transfer pathway from PSII, and thus alleviates PSII excitation pressure by channeling up to 30% of PSII-originated electrons. Furthermore, intact phycobilisomes are required for stable expression of the flv4-2 operon genes and for the Flv2/Flv4 heterodimer-mediated electron transfer mechanism. The latter operates in photoprotection in a complementary way with the orange carotenoid protein-related nonphotochemical quenching. Expression of the flv4-2 operon and exchange of the D1 forms in PSII centers upon light stress, on the contrary, are mutually exclusive photoprotection strategies among cyanobacteria.GlossaryFDPflavodiiron proteinROSreactive oxygen speciesPBphycobilisomeNPQnonphotochemical quenchingLClow CO2HLhigh lightPQplastoquinoneHChigh CO2500-HL500 µmol photons m−2 s−11,500-HL1,500 µmol photons m−2 s−1GLgrowth lightCar/Chl acarotenoid/chlorophyll a ratioDCMU3-(3,4-dichlorophenyl)-1,1-dimethylureaFv/Fmmaximum photochemical efficiency of PSII in the dark-adapted stateY(II)quantum yield of PSIIDMBQ2,6-dimethyl-p-benzoquinoneFmDmaximal fluorescence after initial dark incubationFm′maximum PSII fluorescence in the light-adapted stateF0 risethe transient increase of fluorescence after termination of actinic lightF0fluorescence after termination of actinic lightFvvariable PSII fluorescence in the dark-adapted stateFqFm′ − FsFssteady state fluorescence level in the light-adapted stateQA−negatively charged primary electron-accepting plastoquinone of PSIIOCPorange carotenoid proteinDBMIB2,5-dibromo-3-methyl-6-isopropyl-p-benzoquinoneDCBQ2,6-dichloro-p-benzoquinoneRT-PCRreverse transcription PCR