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A unique ferredoxin acts as a player in the low-iron response of photosynthetic organisms

Schorsch, Michael; Kramer, Manuela; Goss, Tatjana; Eisenhut, Marion; Robinson, Nigel; Osman, Deenah; Wilde, Annegret; Sadaf, Shamaila; Brückler, Hendrik; Walder, Lorenz; Scheibe, Renate; Hase, Toshiharu; Hanke, Guy T.

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Authors

Michael Schorsch

Manuela Kramer

Tatjana Goss

Marion Eisenhut

Deenah Osman

Annegret Wilde

Shamaila Sadaf

Hendrik Brückler

Lorenz Walder

Renate Scheibe

Toshiharu Hase

Guy T. Hanke



Abstract

Iron chronically limits aquatic photosynthesis, especially in marine environments, and the correct perception and maintenance of iron homeostasis in photosynthetic bacteria, including cyanobacteria, is therefore of global significance. Multiple adaptive mechanisms, responsive promoters, and posttranscriptional regulators have been identified, which allow cyanobacteria to respond to changing iron concentrations. However, many factors remain unclear, in particular, how iron status is perceived within the cell. Here we describe a cyanobacterial ferredoxin (Fed2), with a unique C-terminal extension, that acts as a player in iron perception. Fed2 homologs are highly conserved in photosynthetic organisms from cyanobacteria to higher plants, and, although they belong to the plant type ferredoxin family of [2Fe-2S] photosynthetic electron carriers, they are not involved in photosynthetic electron transport. As deletion of fed2 appears lethal, we developed a C-terminal truncation system to attenuate protein function. Disturbed Fed2 function resulted in decreased chlorophyll accumulation, and this was exaggerated in iron-depleted medium, where different truncations led to either exaggerated or weaker responses to low iron. Despite this, iron concentrations remained the same, or were elevated in all truncation mutants. Further analysis established that, when Fed2 function was perturbed, the classical iron limitation marker IsiA failed to accumulate at transcript and protein levels. By contrast, abundance of IsiB, which shares an operon with isiA, was unaffected by loss of Fed2 function, pinpointing the site of Fed2 action in iron perception to the level of posttranscriptional regulation.

Citation

Schorsch, M., Kramer, M., Goss, T., Eisenhut, M., Robinson, N., Osman, D., …Hanke, G. T. (2018). A unique ferredoxin acts as a player in the low-iron response of photosynthetic organisms. Proceedings of the National Academy of Sciences, 115(51), E12111-E12120. https://doi.org/10.1073/pnas.1810379115

Journal Article Type Article
Acceptance Date Nov 5, 2018
Online Publication Date Dec 4, 2018
Publication Date Dec 4, 2018
Deposit Date Nov 6, 2018
Publicly Available Date Jan 4, 2019
Journal Proceedings of the National Academy of Sciences
Print ISSN 0027-8424
Electronic ISSN 1091-6490
Publisher National Academy of Sciences
Peer Reviewed Peer Reviewed
Volume 115
Issue 51
Pages E12111-E12120
DOI https://doi.org/10.1073/pnas.1810379115
Public URL https://durham-repository.worktribe.com/output/1309669

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