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Heterocyst-specific flavodiiron protein Flv3B enables oxic diazotrophic growth of the filamentous cyanobacterium Anabaena sp. PCC 7120
- Ermakova, Maria, Battchikova, Natalia, Richaud, Pierre, Leino, Hannu, Kosourov, Sergey, Isojärvi, Janne, Peltier, Gilles, Flores, Enrique, Cournac, Laurent, Allahverdiyeva, Yagut, Aro, Eva-Mari
- Proceedings of the National Academy of Sciences of the United States of America 2014 v.111 no.30 pp. 11205-11210
- Anabaena, gene expression, nitrogen, nitrogenase, photostability, proteins, vegetative cells
- Flavodiiron proteins are known to have crucial and specific roles in photoprotection of photosystems I and II in cyanobacteria. The filamentous, heterocyst-forming cyanobacterium Anabaena sp. strain PCC 7120 contains, besides the four flavodiiron proteins Flv1A, Flv2, Flv3A, and Flv4 present in vegetative cells, two heterocyst-specific flavodiiron proteins, Flv1B and Flv3B. Here, we demonstrate that Flv3B is responsible for light-induced O ₂ uptake in heterocysts, and that the absence of the Flv3B protein severely compromises the growth of filaments in oxic, but not in microoxic, conditions. It is further demonstrated that Flv3B-mediated photosynthetic O ₂ uptake has a distinct role in heterocysts which cannot be substituted by respiratory O ₂ uptake in the protection of nitrogenase from oxidative damage and, thus, in an efficient provision of nitrogen to filaments. In line with this conclusion, the Δ flv3B strain has reduced amounts of nitrogenase NifHDK subunits and shows multiple symptoms of nitrogen deficiency in the filaments. The apparent imbalance of cytosolic redox state in Δ flv3B heterocysts also has a pronounced influence on the amounts of different transcripts and proteins. Therefore, an O ₂-related mechanism for control of gene expression is suggested to take place in heterocysts.