The interplay between autophagy and chloroplast vesiculation pathways
under dark-induced senescence
Abstract
In cellular circumstances where carbohydrates are scarce, plants can use
alternative substrates for cellular energetic maintenance. In plants,
the main protein reserve is present in the chloroplast, which contains
most of the total leaf proteins and represents a rich source of nitrogen
and amino acids. Autophagy plays a key role in chloroplast breakdown, a
well-recognized symptom of both natural and stress-induced plant
senescence. Remarkably, an autophagic-independent route of chloroplast
degradation associated with Chloroplast Vesiculation (CV) gene was
recently demonstrated. During extended darkness, CV is highly induced in
the absence of autophagy, contributing to the early senescence phenotype
of atg mutants. To further investigate the role of CV under
dark-induced senescence conditions, mutants with low expression of CV (
amircv) and double mutants amircv1xatg5 were
characterized. Following darkness treatment, no aberrant phenotypes were
observed in amircv single mutants; however, amircv1xatg5
double mutants displayed early senescence and enhanced dismantling of
chloroplast and membrane structures under these conditions. Metabolic
characterization revealed that the functional lack of both CV and
autophagy leads to higher impairment of amino acid release and
differential organic acid accumulation during starvation conditions. The
data obtained are discussed in the context of the role of CV and
autophagy, both in terms of cellular metabolism and the regulation of
chloroplast degradation.