Abstract
Concepts of organelle-to-nucleus signalling pathways are largely based on genetic screens involving inhibitors of chloroplast and mitochondrial functions such as norflurazon, lincomycin (LINC), antimycin A (ANT) and salicylhydroxamic acid. These inhibitors favour enhanced cellular oxidation, but their precise effects on the cellular redox state are unknown. Using the in vivo reduction–oxidation (redox) reporter, roGFP2, inhibitor-induced changes in the glutathione redox potentials of the nuclei and cytosol were measured in Arabidopsis thaliana root, epidermal and stomatal guard cells, together with the expression of nuclear-encoded chloroplast and mitochondrial marker genes. All the chloroplast and mitochondrial inhibitors increased the degree of oxidation in the nuclei and cytosol. However, inhibitor-induced oxidation was less marked in stomatal guard cells than in epidermal or root cells. Moreover, LINC and ANT caused a greater oxidation of guard cell nuclei than the cytosol. Chloroplast and mitochondrial inhibitors significantly decreased the abundance of LHCA1 and LHCB1 transcripts. The levels of WHY1, WHY3 and LEA5 transcripts were increased in the presence of inhibitors. Chloroplast inhibitors decreased AOXA1 mRNA levels, while mitochondrial inhibitors had the opposite effect. Inhibitors that are used to characterize retrograde signalling pathways therefore have similar general effects on cellular redox state and gene expression.This article is part of the themed issue ‘Enhancing photosynthesis in crop plants: targets for improvement’.
Highlights
Organelle-to-nucleus retrograde signalling pathways coordinate nuclear gene expression with chloroplast and mitochondrial functions
Examples of the images of the primary root cells and the epidermal and stomatal guard cells in the cotyledons of the 5-day-old seedlings that were used to determine the effects of the different inhibitors on the redox sate of the nuclei and cytosol are shown in figure 1
The highest overall increase in oxidation was observed in the LINC þ NF treatment, where the nuclei and cytosol were oxidized to similar levels relative to controls
Summary
Organelle-to-nucleus retrograde signalling pathways coordinate nuclear gene expression with chloroplast and mitochondrial functions. Precise coordination of the expression of genes encoded by the genomes in the different intracellular compartments is required to facilitate the assembly of functional mitochondria and chloroplasts under fluctuating environmental or metabolic conditions [1,2,3]. Much of our current understanding of chloroplast-to-nucleus signalling pathways comes from the characterization of Arabidopsis thaliana genomes uncoupled (gun) mutants [6]. These mutants were isolated using a screen involving exposure to the phytoene desaturase inhibitor, norflurazon (NF). NF-dependent inhibition of carotenoid biosynthesis results in decreased expression of nuclear genes encoding chloroplast proteins, such as the photosynthetic light-harvesting antenna
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