New Arabidopsis thaliana Cytochrome c Partners: A Look Into the Elusive Role of Cytochrome c in Programmed Cell Death in Plants

Abstract

Programmed cell death is an event displayed by many different organisms along the evolutionary scale. In plants, programmed cell death is necessary for development and the hypersensitive response to stress or pathogenic infection. A common feature in programmed cell death across organisms is the translocation of cytochrome c from mitochondria to the cytosol. To better understand the role of cytochrome c in the onset of programmed cell death in plants, a proteomic approach was developed based on affinity chromatography and using Arabidopsis thaliana cytochrome c as bait. Using this approach, ten putative new cytochrome c partners were identified. Of these putative partners and as indicated by bimolecular fluorescence complementation, nine of them bind the heme protein in plant protoplasts and human cells as a heterologous system. The in vitro interaction between cytochrome c and such soluble cytochrome ctargets was further corroborated using surface plasmon resonance. Taken together, the results obtained in the study indicate that Arabidopsis thaliana cytochrome c interacts with several distinct proteins involved in protein folding, translational regulation, cell death, oxidative stress, DNA damage, energetic metabolism, and mRNA metabolism. Interestingly, some of these novel Arabidopsis thaliana cytochrome c-targets are closely related to those for Homo sapiens cytochrome c (Martínez-Fá bregas et al., unpublished). These results indicate that the evolutionarily well-conserved cytosolic cytochrome c, appearing in organisms from plants to mammals, interacts with a wide range of targets on programmed cell death.

Structural and Functional Analysis of Novel Human Cytochrome c Targets in Apoptosis

“…The findings can open up new ways to understand the process in organisms that lack Apaf-1 or whose apoptosome is devoid of Cc. Given that Cc is highly concentrated in the mitochondrial intermembrane space and that its release into the cytoplasm is an evolutionarily well-conserved event, it is likely that Cc regulates other metabolic processes during PCD, as has been similarly corroborated in plants (105).…”

Respiratory complexes III and IV can each bind two molecules of cytochrome c at low ionic strength

“…The organization of the mitochondrial electron transport chain is a subject of intense debate at present, where two different models are being considered: the fluid model, that proposes a random organization for individual respiratory protein components, and the solid model, suggesting a stable association between individual complexes [6][7][8]. Apart their role in respiration, Cc and Cc 1 are clearly involved in the development of programmed cell death [9][10][11][12][13][14][15]. Such a dual role of Cc is regulated by post-translational modifications -namely, phosphorylation and nitration of tyrosine residues -that affect the binding of Cc to its physiological counterparts, either in the mitochondria or in the cytoplasm [16][17][18][19][20][21][22][23].…”

Structural basis of mitochondrial dysfunction in response to cytochrome c phosphorylation at tyrosine 48

“…In mammalian cells, extramitochondrial Cc interacts with apoptosis activating factor 1 (Apaf-1) in the cytoplasm to spark the caspase proteolytic cascade (15). It has recently been shown that Cc can interact with several other proteins outside the mitochondria in humans and plants (18)(19)(20)(21). The similarities between the Cc signaling networks in both organisms suggest that key programmed cell-death pathways are conserved throughout evolution (22).…”

“…In addition, Cc aids in controlling ROS levels by oxidizing superoxide anions (11) and exhibiting peroxidase activity (12); the latter, however, also yields lipid peroxidation (13,14). Furthermore, Cc plays a crucial role in programmed cell death, a process that is only partially understood (15)(16)(17)(18)(19)(20)(21). In this context, a fraction of Cc binds and oxidizes cardiolipin (CL) at the internal mitochondrial membrane, thereby facilitating the release of unbound Cc to the cytoplasm (16,17).…”