Dynamic Changes of IsiA-Containing Complexes during Long-Term Iron Deficiency in Synechocystis sp. PCC 6803

Abstract

Iron stress-induced protein A (IsiA), a major chlorophyll-binding protein in the thylakoid membrane, is significantly induced under iron deficiency conditions. Using immunoblot analysis and 77 K fluorescence spectroscopy combined with sucrose gradient fractionation, we monitored dynamic changes of IsiA-containing complexes in Synechocystis sp. PCC 6803 during exposure to long-term iron deficiency. Within 3 days of exposure to iron deficiency conditions, the initially induced free IsiA proteins preferentially conjugated to PS I trimer to form IsiA-PS I trimers, which serve as light energy collectors for efficiently transmitting energy to PS I. With prolonged iron deficiency, IsiA proteins assembled either into IsiA aggregates or into two other types of IsiA-PS I supercomplexes, namely IsiA-PS I high fluorescence supercomplex (IHFS) and IsiA-PS I low fluorescence supercomplex (ILFS). Further analysis revealed a role for IsiA as an energy dissipater in the IHFS and as an energy collector in the ILFS. The trimeric structure of PS I mediated by PsaL was found to be indispensable for the formation of IHFS/ILFS. Dynamic changes in IsiA-containing complexes in cyanobacteria during long-term iron deficiency may represent an adaptation to iron limitation stress for flexible light energy distribution, which balances electron transfer between PS I and PS II, thus minimizing photooxidative damage.

Resequencing of a mutant bearing an iron starvation recovery phenotype defines Slr1658 as a new player in the regulatory network of a model cyanobacterium

“…Growth did not resume, photosystem I (PSI) activity remained low and IsiA fluorescence remained high. IsiA is an iron‐regulated chlorophyll a ‐binding protein which can act as an antenna when bound to PSI but can also dissipate absorbed light energy (Chen and Bibby, ; Ryan‐Keogh et al ., ; Ma et al ., ).…”

A unique porin meditates iron‐selective transport through cyanobacterial outer membranes

“…It has been well established that PSI is one of largest iron sinks in cyanobacteria and is degraded during Fe limitation (Raven et al ., 1999; Ma et al ., 2017; Schoffman and Keren, 2019). In line with the response characteristic of iron limitation, slr1908 KD exhibited decreased PSI content under Fe‐replete conditions (Fig.…”

“…2E). After sucrose gradient ultracentrifugation, the thylakoid membrane sample of Synechocystis separates into three pigmented fractions: a free pigment fraction (F1), a fraction containing PSI monomers and PSII (F2), and a trimeric PSI fraction (F3) (Ma et al ., 2017). The pigment‐protein complexes in F2 and F3 where further identified by 77 K chlorophyll emission spectra (Fig.…”

Regulatory sRNAs in Cyanobacteria

“…Cyanobacteria constitute a wide variety of photoautotrophic bacteria that undergo oxygenic photosynthesis and grow under extremely diverse environmental conditions on Earth, such as oceans, freshwater, rocks surface, desert soils, or even polar regions. The existence of cyanobacteria can be traced back possibly up to 3–5 billion years ( Schopf, 1993 ), and they have long been recognized as important model organisms for research in aspects such as photosynthesis ( Pisciotta et al, 2010 ; Chen et al, 2015 ), metabolism ( Tamagnini et al, 2002 ), stress responses ( Wang et al, 2008 ; Ma et al, 2017 ), biotechnology ( Abed et al, 2009 ; Zhan and Wang, 2018 ), evolution ( Flores and Herrero, 2008 ), and nitrogen fixation ( Goebel et al, 2010 ). Particularly, cyanobacteria are a group of unicellular aquatic prokaryotes that possess certain properties such as fast growth, short life cycle, and spontaneously transformability, which have entitled them to be one of simple experimental systems and the most promising feedstock for bioenergy generation ( Quintana et al, 2011 ; Giordano and Wang, 2018 ).…”