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Pyridine nucleotide transhydrogenase Pnt AB is essential for optimal growth and photosynthetic integrity under low‐light mixotrophic conditions in Synechocystis sp. PCC 6803
Author(s) -
Kämäräinen Jari,
Huokko Tuomas,
Kreula Sanna,
Jones Patrik R.,
Aro EvaMari,
Kallio Pauli
Publication year - 2017
Publication title -
new phytologist
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 3.742
H-Index - 244
eISSN - 1469-8137
pISSN - 0028-646X
DOI - 10.1111/nph.14353
Subject(s) - synechocystis , biochemistry , nad+ kinase , mixotroph , biology , autotroph , photosynthesis , mutant , cyanobacteria , heterotroph , bacteria , gene , enzyme , genetics
Summary Pyridine nucleotide transhydrogenase (Pnt AB ) is an integral membrane protein complex participating in the regulation of NAD (P) + : NAD (P)H redox homeostasis in various prokaryotic and eukaryotic organisms. In the present study we addressed the function and biological role of Pnt AB in oxygenic photosynthetic cyanobacteria capable of both autotrophic and heterotrophic growth, with support from structural three‐dimensional (3D)‐modeling. The pntA gene encoding the α subunit of heteromultimeric Pnt AB in Synechocystis sp. PCC 6803 was inactivated, followed by phenotypic and biophysical characterization of the Δ pntA mutant under autotrophic and mixotrophic conditions. Disruption of pntA resulted in phenotypic growth defects observed under low light intensities in the presence of glucose, whereas under autotrophic conditions the mutant did not differ from the wild‐type strain. Biophysical characterization and protein‐level analysis of the Δ pntA mutant revealed that the phenotypic defects were accompanied by significant malfunction and damage of the photosynthetic machinery. Our observations link the activity of Pnt AB in Synechocystis directly to mixotrophic growth, implicating that under these conditions Pnt AB functions to balance the NADH : NADPH equilibrium specifically in the direction of NADPH . The results also emphasize the importance of NAD (P) + : NAD (P)H redox homeostasis and associated ATP : ADP equilibrium for maintaining the integrity of the photosynthetic apparatus under low‐light glycolytic metabolism.