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The cyanobacterial chlorophyll-binding-protein IsiA acts to increase the in vivo effective absorption cross-section of PSI under iron limitation

The cyanobacterial chlorophyll-binding-protein IsiA acts to increase the in vivo effective absorption cross-section of PSI under iron limitation
The cyanobacterial chlorophyll-binding-protein IsiA acts to increase the in vivo effective absorption cross-section of PSI under iron limitation
Iron availability limits primary production in >30% of the world’s oceans; hence phytoplankton have developed acclimation strategies. In particular, cyanobacteria express IsiA (iron-stress-induced) under iron stress, which can become the most abundant chl-binding protein in the cell. Within iron-limited oceanic regions with significant cyanobacterial biomass, IsiA may represent a significant fraction of the total chl. We spectroscopically measured the effective cross-section of the photosynthetic reaction center PSI (?PSI) in vivo and biochemically quantified the absolute abundance of PSI, PSII, and IsiA in the model cyanobacterium Synechocystis sp. PCC 6803. We demonstrate that accumulation of IsiA results in a ?60% increase in ?PSI, in agreement with the theoretical increase in cross-section based on the structure of the biochemically isolated IsiA-PSI supercomplex from cyanobacteria. Deriving a chl budget, we suggest that IsiA plays a primary role as a light-harvesting antenna for PSI. On progressive iron-stress in culture, IsiA continues to accumulate without a concomitant increase in ?PSI, suggesting that there may be a secondary role for IsiA. In natural populations, the potential physiological significance of the uncoupled pool of IsiA remains to be established. However, the functional role as a PSI antenna suggests that a large fraction of IsiA-bound chl is directly involved in photosynthetic electron transport.
chlorophyll-binding protein, cyanobacteria, iron limitation, IsiA, PSI
1529-8817
145-154
Ryan-Keogh, Thomas J.
86e4ee72-2e27-4f45-a579-6edb67de4ac4
Macey, Anna I.
04c3fff6-93ca-437c-8280-a94cc10f7fed
Cockshutt, Amanda M.
88de6c9e-e49d-45b2-b504-850486c33378
Moore, C. Mark
7ec80b7b-bedc-4dd5-8924-0f5d01927b12
Bibby, Thomas S.
e04ea079-dd90-4ead-9840-00882de27ebd
Ryan-Keogh, Thomas J.
86e4ee72-2e27-4f45-a579-6edb67de4ac4
Macey, Anna I.
04c3fff6-93ca-437c-8280-a94cc10f7fed
Cockshutt, Amanda M.
88de6c9e-e49d-45b2-b504-850486c33378
Moore, C. Mark
7ec80b7b-bedc-4dd5-8924-0f5d01927b12
Bibby, Thomas S.
e04ea079-dd90-4ead-9840-00882de27ebd

Ryan-Keogh, Thomas J., Macey, Anna I., Cockshutt, Amanda M., Moore, C. Mark and Bibby, Thomas S. (2012) The cyanobacterial chlorophyll-binding-protein IsiA acts to increase the in vivo effective absorption cross-section of PSI under iron limitation. Journal of Phycology, 48 (1), 145-154. (doi:10.1111/j.1529-8817.2011.01092.x).

Record type: Article

Abstract

Iron availability limits primary production in >30% of the world’s oceans; hence phytoplankton have developed acclimation strategies. In particular, cyanobacteria express IsiA (iron-stress-induced) under iron stress, which can become the most abundant chl-binding protein in the cell. Within iron-limited oceanic regions with significant cyanobacterial biomass, IsiA may represent a significant fraction of the total chl. We spectroscopically measured the effective cross-section of the photosynthetic reaction center PSI (?PSI) in vivo and biochemically quantified the absolute abundance of PSI, PSII, and IsiA in the model cyanobacterium Synechocystis sp. PCC 6803. We demonstrate that accumulation of IsiA results in a ?60% increase in ?PSI, in agreement with the theoretical increase in cross-section based on the structure of the biochemically isolated IsiA-PSI supercomplex from cyanobacteria. Deriving a chl budget, we suggest that IsiA plays a primary role as a light-harvesting antenna for PSI. On progressive iron-stress in culture, IsiA continues to accumulate without a concomitant increase in ?PSI, suggesting that there may be a secondary role for IsiA. In natural populations, the potential physiological significance of the uncoupled pool of IsiA remains to be established. However, the functional role as a PSI antenna suggests that a large fraction of IsiA-bound chl is directly involved in photosynthetic electron transport.

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More information

Published date: February 2012
Keywords: chlorophyll-binding protein, cyanobacteria, iron limitation, IsiA, PSI
Organisations: Ocean Biochemistry & Ecosystems

Identifiers

Local EPrints ID: 300728
URI: http://eprints.soton.ac.uk/id/eprint/300728
ISSN: 1529-8817
PURE UUID: f475d40a-4b1d-4f3c-8f60-43d37342d47b
ORCID for C. Mark Moore: ORCID iD orcid.org/0000-0002-9541-6046

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Date deposited: 24 Feb 2012 10:43
Last modified: 15 Mar 2024 03:03

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Contributors

Author: Thomas J. Ryan-Keogh
Author: Anna I. Macey
Author: Amanda M. Cockshutt
Author: C. Mark Moore ORCID iD
Author: Thomas S. Bibby

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