Pseudo-reversion of the high-CO2 requiring phenotype of
the NADH dehydrogenase type 1-impaired mutant of
Synechocystis PCC6803, strain M55, by salt stress
coincides with partial restoration of PSI-driven cyclic electron transfer. In
M55, the complete family of D proteins (D1–D6) that are needed for
electron transfer through the complex is lacking. Adaptation to salt stress
requires de novo synthesis of full-length 47-kDa
ferredoxin-NADP+ reductase (FNR). A mutant created
in the M55 background, which only expresses truncated chloroplast 37-kDa FNR
cannot adapt to salt stress and refrains from growth in low
CO2. A special feature of FNR in cyanobacteria is the
relatively high molecular mass of 44–48 kDa. A positively charged
extended N-terminal domain of the cyanobacterial enzyme
defines the extra mass. The extension likely plays a key role in the
salt-stress inducible enhancement of PSI-driven cyclic electron transfer, and
in the pseudo-reversion of the high-CO2 requiring
phenotype of M55. Data acquired with several other cyanobacteria and the
oxychlorobacterium Prochlorothrix hollandica contributed
to the present hypothesis. It proposes that FNR is involved in regulation of
inducible and transient PSI cyclic electron transfer in cyanobacteria via a
thylakoid surface charge and conditional-proteolysis steered mechanism.
Going with the Electron Flow: Heme Electronic Structure and Electron Transfer in Cytochromec