Comparative analysis of idiA and isiA transcription under iron starvation and oxidative stress in Synechococcus elongatus PCC 7942 wild-type and selected mutants.
In the mesophilic cyanobacterium Synechococcus elongatus PCC 7942, iron starvation induces the expression of a number of proteins, including IdiA and IsiA. Whereas IdiA protects photosystem (PS) II under mild iron limitation against oxidative stress in a yet unknown way, prolonged iron starvation leads to the formation of the PS I-IsiA supercomplex. Transcription of idiA is positively regulated by IdiB under iron starvation, and Fur represses transcription of isiAB under iron-sufficient growth conditions. In this report, data are presented suggesting a strong interrelationship between iron homeostasis and oxidative stress in S. elongatus PCC 7942, and showing that transcription of major iron-regulated genes, such as isiA, isiAB, idiA, idiB, mapA, and irpA, is induced by oxidative stress within a few minutes by treatment of cells with hydrogen peroxide or methylviologen. The overall results suggest that isiA/isiAB as well as idiB transcription in response to oxidative stress might be controlled by a transcriptional repressor possibly of the PerR-type. This fact also explains the observed cross-talk between IdiB- and Fur-mediated transcriptional regulation of gene expression and for the role of H(2)O(2) as a superior trigger coordinating expression of iron-regulated genes under iron starvation and oxidative stress. Measuring 77 K chlorophyll a fluorescence, it is shown that hydrogen peroxide treatment causes a transient short-term modification of PS II and PS I most likely leading to increased cyclic electron transport around PS I. In this context, the intriguing observation was made that idiB is transcribed as part of an operon together with a gene encoding a potential [2Fe-2S]-protein. This protein has similarity to [Fe-S]-proteins involved in the electron transport activity of the NDH I complex in eubacteria. Since the NDH I complex is involved in cyclic electron transport activity around PS I in cyanobacteria and both adaptation to iron starvation and adaptation to oxidative stress lead to an enhanced cyclic electron transport activity around PS I, this potential [Fe-S]-protein might participate in the overall adaptational response to iron starvation and/or oxidative stress in Synechococcus.
Yousef
Naeima
N
Biologie VIII: Molekulare Zellphysiologie, Universität Bielefeld, 33615 Bielefeld, Germany.
Pistorius
Elfriede K
EK
Michel
Klaus-Peter
KP
D001426:Bacterial Proteins / Q000032:analysis / Q000235:genetics*; D002734:Chlorophyll / Q000737:chemistry; D000077194:Chlorophyll A; D000458:Cyanobacteria / Q000235:genetics* / Q000378:metabolism*; D005418:Flavodoxin / Q000235:genetics; D005453:Fluorescence; D015964:Gene Expression Regulation, Bacterial; D006861:Hydrogen Peroxide / Q000378:metabolism; D007501:Iron / Q000378:metabolism*; D033862:Iron-Binding Proteins / Q000032:analysis / Q000235:genetics*; D045342:Light-Harvesting Protein Complexes / Q000235:genetics*; D008565:Membrane Proteins / Q000235:genetics; D016366:Open Reading Frames; D009876:Operon / Q000235:genetics / Q000502:physiology; D018384:Oxidative Stress; D010269:Paraquat / Q000378:metabolism; D045331:Photosystem I Protein Complex / Q000502:physiology; D012333:RNA, Messenger / Q000032:analysis; D012097:Repressor Proteins / Q000235:genetics; D013057:Spectrum Analysis; D014157:Transcription Factors / Q000235:genetics; D014158:Transcription, Genetic
D001426:Bacterial Proteins; D005418:Flavodoxin; C102679:IdiA protein, Synechococcus; C434050:IdiB protein, Synechococcus; D033862:Iron-Binding Proteins; D045342:Light-Harvesting Protein Complexes; D008565:Membrane Proteins; D045331:Photosystem I Protein Complex; D012333:RNA, Messenger; D012097:Repressor Proteins; D014157:Transcription Factors; C068477:ferric uptake regulating proteins, bacterial; D002734:Chlorophyll; C076726:chlorophyll A binding protein CP43, Cyanobacteria; D006861:Hydrogen Peroxide; D007501:Iron; D010269:Paraquat; D000077194:Chlorophyll A