Abstract
Retrograde signalling refers to the regulation of nuclear gene expression in response to functional changes in organelles. In plants, the two energy-converting organelles, mitochondria and chloroplasts, are tightly coordinated to balance their activities. Although our understanding of components involved in retrograde signalling has greatly increased in the last decade, studies on the regulation of the two organelle signalling pathways have been largely independent. Thus, the mechanism of how mitochondrial and chloroplastic retrograde signals are integrated is largely unknown. Here, we summarize recent findings on the function of mitochondrial signalling components and their links to chloroplast retrograde responses. From this, a picture emerges showing that the major regulators are integrators of both organellar retrograde signalling pathways.This article is part of the theme issue ‘Retrograde signalling from endosymbiotic organelles’.
Highlights
The retrograde response pathway initiates a signalling cascade to modulate the expression of nuclear genes in response to changes in mitochondrial and chloroplastic function
The biochemical, cellular and physiological reasons why mitochondrial and chloroplast retrograde signalling may be linked at several levels are worth considering
Chloroplasts and mitochondria have emerged as environmental sensors to ensure that the 8 pipeline from gene expression to protein function is optimized relative to organelle function
Summary
The retrograde response pathway initiates a signalling cascade to modulate the expression of nuclear genes in response to changes in mitochondrial and chloroplastic function. The facts that ANAC017 is not inducible at a transcript level and is present in a latent form [38], overexpression of ANAC017 results in early senescence [40], the existence of several negative regulators of AOX1a [43] and the recent demonstration that RADICAL-INDUCED CELL DEATH PROTEIN1 (RCD1) binds to ANAC017 to suppress its activity [33] (figure 1) together show that while mitochondrial retrograde signalling is important for environmental stress responses, it is kept highly suppressed under non-limiting growth conditions. The transcript of At12Cys-2 was highly induced in ANAC013 overexpression lines and the induction after AA treatment was dramatically diminished in lines with reduced ANAC013 expression (ANAC013-miR) [41] These results indicate that ANAC013 is a positive regulator of the At12Cys-2-dependent retrograde signalling pathway. One possible candidate is RRL, which is required for the increase in protein abundance downstream of mitochondrial signalling ([83])
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