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.
Highlights
The chloroplast, a well-known plastid found in all photosynthetic plant cells, is the central organelle providing plants with foods and energy in the form of sugar or starch by photosynthesis (Jarvis and Lopez-Juez, 2014)
To cope with a variety of internal or external stresses, plants carry out leaf senescence via selective degradation of chloroplasts to avoid the accumulation of toxic ROS, placing a significance of efficient chloroplast turnover under stress conditions (Xie et al, 2015; Izumi and Nakamura, 2018; Nakamura and Izumi, 2018; Otegui, 2018; Soto-Burgos et al, 2018)
Novel insights into our understanding of chloroplast turnover have been obtained by recent studies on the relationship between chloroplast degradation and autophagy, a self-eating process conserved in all eukaryotic cells (Liu and Bassham, 2012)
Summary
The chloroplast, a well-known plastid found in all photosynthetic plant cells, is the central organelle providing plants with foods and energy in the form of sugar or starch by photosynthesis (Jarvis and Lopez-Juez, 2014). Microautophagy can be either ATG-dependent or ATGindependent (Mijaljica et al, 2011; Oku et al, 2017) These different types of autophagy have been implicated in cargo selectivity to facilitate the bulk or specific degradation of the target cargos under different conditions. Excellent reviews have implicated that both macroautophagy and microautophagy pathways contribute to chloroplast degradation, and exhibit cargo specificity under different types of conditions (e.g., leaf senescence, carbon starvation or high light stress) by forming various types of structures (Xie et al, 2015; Izumi and Nakamura, 2018; Nakamura and Izumi, 2018; Otegui, 2018; Soto-Burgos et al, 2018). Several types of macroautophagyrelated structures have been reported, including the Rubiscocontaining body (RCB) (Ishida et al, 2008), the ATI1GFP Labels Plastid-Associated Body (ATI-PS body) (Michaeli et al, 2014), and small starch granule-like structures (SSTG) (Wang Y. et al, 2013; Figure 1)
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