Chloroplast Degradation: Multiple Routes Into the Vacuole

Abstract

Chloroplasts provide energy for all plants by producing sugar during photosynthesis. To adapt to various environmental and developmental cues, plants have developed specific strategies to control chloroplast homeostasis in plant cells, including chloroplast degradation during leaf senescence and the transition of chloroplasts into other types of plastids during the day-night cycle. In recent years, autophagy has emerged as an essential mechanism for selective degradation of chloroplast materials (also known as chlorophagy) in the vacuole. Different types of membrane structures have been implicated to involve in the delivery of distinct chloroplast contents. Here we provide a current overview on chlorophagy and discuss the possible chloroplast receptors and upstream signals in this process.

Abscisic Acid and Jasmonate Metabolisms Are Jointly Regulated During Senescence in Roots and Leaves of Populus trichocarpa

“…In LS2, chlorophyll autofluorescence was barely visible, suggesting that the majority of these organelles had been degraded. These observations are in agreement with recent findings on the role of ABA in chlorophagy [61,62]. In that study, the stromule number increased in response to an ABA treatment, whereas treatment with a specific inhibitor of ABA synthesis prevented the formation of stromules by mannitol [61].…”

“…In that study, the stromule number increased in response to an ABA treatment, whereas treatment with a specific inhibitor of ABA synthesis prevented the formation of stromules by mannitol [61]. Moreover, it has been suggested that proteins belonging to kinase family (SnRK2, CK2), which are activated by the ABA signaling pathway, might participate in phosphorylation of chloroplast membrane proteins or the ATG proteins and activate chlorophagy [62,63].…”

Autophagy: An Intracellular Degradation Pathway Regulating Plant Survival and Stress Response

“…Similarly, chloroplasts damaged by strong light or ultraviolet-B are also subjected to degradation through autophagy (Izumi et al, 2017). Chlorophagy happens in many ways, including the whole chloroplast, the Rubisco containing body (RCB), the ATI1-GFP labels plastid-associated body (ATI-PS body), and the small starch granule-like structures pathways Nakamura et al, 2019;Zhuang and Jiang, 2019).…”

Proanthocyanidin Biosynthesis—a Matter of Protection

“…An alternative approach is to apply new tools to existing models. Autophagy of chloroplasts can occur through multiple routes, including the process of microchlorophagy in which more than one type of small vesicle can be targeted to the main vacuole (Zhuang and Jiang, 2019). Monitoring this process during the early developmental stages of the Arabidopsis seed coat endothelium, where PA synthesis occurs, could provide a means of testing the tannosome model in a genetically tractable system.…”