Michel Klaus-Peter, Pistorius Elfriede K.
Biologie VIII: Molekulare Zellphysiologie, Universität Bielefeld, D-33501 Bielefeld, Germany.
Physiol Plant. 2004 Jan;120(1):36-50. doi: 10.1111/j.0031-9317.2004.0229.x.
In this review we give an overview on the adaptational responses of photosystem (PS) II and PSI in cyanobacteria to iron starvation, mainly summarizing our results with the mesophilic Synechococcus elongatus PCC 7942. We also discuss this process with respect to the strong interrelationship between iron limitation and oxidative stress that exists in cyanobacteria as oxygenic photosynthetic organisms. The adaptation of the multiprotein complexes PSII and PSI to iron starvation is a sequential process, which is characterized by the enhanced expression of two major iron-regulated proteins, IdiA (iron deficiency induced protein A) and IsiA (iron stress induced protein A). Our results suggest that IdiA protects the acceptor side of PSII against oxidative stress under conditions of mild iron limitation in a currently unclear way, whereas prolonged iron deficiency leads to the synthesis of a chlorophyll a antenna around PSI-trimers consisting of IsiA molecules. The physiological consequences of these alterations under prolonged iron starvation, as shown by acridine yellow fluorescence measurements, are a reduction of linear electron transport activity through PSII and an increase of cyclic electron flow around PSI as well as an increase in respiratory activity. IdiA and IsiA expression are mediated by two distinct helix-turn-helix transcriptional regulators of the Crp/Fnr family. IdiB positively regulates expression of idiA under iron starvation, and Fur represses transcription of isiA under iron-sufficient conditions. Although both transcriptional regulators seem to operate independently of each other, our results indicate that a cross-talk between the signal transduction pathways exists. Moreover, IdiA as well as IsiA expression are affected by hydrogen peroxide. We suggest that due to the interdependence of iron limitation and the formation of reactive oxygen species, peroxide stress might be the superior trigger that leads to expression of these proteins under iron starvation. The modifications of PSII and PSI under iron starvation influence the redox state of redox-sensitive components of the electron transport chain, and thus the activity of metabolic pathways being regulated in dependence of the redox state of these components.
在本综述中，我们概述了蓝细菌中光系统（PS）II和PSI对铁饥饿的适应性反应，主要总结了我们对嗜温性聚球藻PCC 7942的研究结果。我们还结合铁限制与氧化应激之间的紧密相互关系来讨论这一过程，这种关系存在于作为产氧光合生物的蓝细菌中。多蛋白复合物PSII和PSI对铁饥饿的适应是一个循序渐进的过程，其特征是两种主要的铁调节蛋白，即IdiA（缺铁诱导蛋白A）和IsiA（铁应激诱导蛋白A）的表达增强。我们的结果表明，在轻度铁限制条件下，IdiA以目前尚不清楚的方式保护PSII的受体侧免受氧化应激，而长期缺铁会导致由IsiA分子组成的围绕PSI三聚体的叶绿素a天线的合成。吖啶黄荧光测量结果表明，长期铁饥饿条件下这些变化的生理后果是通过PSII的线性电子传递活性降低、围绕PSI的循环电子流增加以及呼吸活性增强。IdiA和IsiA的表达由Crp/Fnr家族的两种不同的螺旋-转角-螺旋转录调节因子介导。IdiB在铁饥饿条件下正向调节idiA的表达，而Fur在铁充足条件下抑制isiA的转录。尽管这两种转录调节因子似乎相互独立发挥作用，但我们的结果表明信号转导途径之间存在相互作用。此外，IdiA以及IsiA的表达都受到过氧化氢的影响。我们认为，由于铁限制与活性氧形成的相互依存关系，过氧化物应激可能是导致这些蛋白质在铁饥饿条件下表达的主要触发因素。铁饥饿条件下PSII和PSI的修饰会影响电子传递链中氧化还原敏感成分的氧化还原状态，进而影响依赖于这些成分氧化还原状态进行调节的代谢途径的活性。
