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‐recognised symptom of both natural and stress‐induced plant senescence. Remarkably, an autophagic‐independent route of chloroplast degradation associated with chloroplast vesiculation (CV) gene was previously 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 characterised. Following darkness treatment, no aberrant phenotypes were observed in amircv single mutants; however, amircv1xatg5 double mutants displayed early senescence and altered dismantling of chloroplast and membrane structures under these conditions. Metabolic characterisation 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.

Osmotic stress in roots drives lipoxygenase-dependent plastid remodeling through singlet oxygen production

“…In dark stressed green tissue, an autophagosomal-dependent process produces small Rubisco-containing bodies that are pinched off from the chloroplast (Ishida et al, 2008). Additionally, there exists an autophagy-independent chloroplast vesiculation pathway that produces vesicles within the chloroplast, as well as extraplastidic bodies containing both stromal and thylakoid membrane proteins (Wang and Blumwald, 2014) In both cases the bodies are targeted to the vacuoles for turnover of their contents to ameliorate starvation conditions (Barros et al, 2023). The extraplastidic bodies shown here may merge with the vacuole as shown in Figure 2 A and are thus involved in membrane turnover.…”