Commonalities and differences in plants deficient in autophagy and alternative pathways of respiration on response to extended darkness

Abstract

Autophagy is a highly conserved cellular mechanism in eukaryotes allowing the degradation of cell constituents. It is of crucial significance in both cellular homeostasis and nutrient recycling. During energy limited conditions plant cells can metabolize alternative respiratory substrates, such as amino acids, providing electrons to the mitochondrial metabolism via the tricarboxylic acid (TCA) cycle or electron transfer flavoprotein/ electron transfer flavoprotein ubiquinone oxidoreductase (ETF/ETFQO) system. Our recent study reveals the importance of autophagy in the supply of amino acids to provide energy through alternative pathways of respiration during carbon starvation. This fact apart, autophagy seems to have more generalized effects related not only to amino acid catabolism but also to metabolism in general. By further comparing the metabolic data obtained with atg mutants with those of mutants involved in the alternative pathways of respiration, we observed clear differences between these mutants, pointing out additional effects of the autophagy deficiency on metabolism of Arabidopsis leaves. Collectively, our data point to an interdependence between mitochondrial metabolism and autophagy and suggest an exquisite regulation of primary metabolism under low energetic conditions.

Keywords: Alternative pathways; ETF/ETFQO pathway; autophagy; energy deprivation; metabolite profiling.

Figure 1.

Differential metabolic response between atg and alternative respiratory pathway mutants under darkness-induced treatment. (A) Principal component analysis (PCA) was performed using the metabolic data of autophagy and alternative pathways prior (open squares) and after 9-10 days of dark treatment (closed squares). The respective mutants symbols are indicated in the figure; wt and wt2 are corresponds to control background for atg and eftqo mutants respectively. (B) Venn diagrams illustrates the metabolites that significantly increased (left) or decreased (right) at the 5% level in atg and etfqo mutants in relation to respective wild type after darkness treatment.