Regulation of Chlorophagy during Photoinhibition and Senescence: Lessons from Mitophagy

Light energy is essential for photosynthetic energy production and plant growth. Chloroplasts in green tissues convert energy from sunlight into chemical energy via the electron transport chain. When the level of light energy exceeds the capacity of the photosynthetic apparatus, chloroplasts undergo a process known as photoinhibition. Since photoinhibition leads to the overaccumulation of reactive oxygen species (ROS) and the spreading of cell death, plants have developed multiple systems to protect chloroplasts from strong light. Recent studies have shown that autophagy, a system that functions in eukaryotes for the intracellular degradation of cytoplasmic components, participates in the removal of damaged chloroplasts. Previous findings also demonstrated an important role for autophagy in chloroplast turnover during leaf senescence. In this review, we describe the turnover of whole chloroplasts, which occurs via a type of autophagy termed chlorophagy. We discuss a possible regulatory mechanism for the induction of chlorophagy based on current knowledge of photoinhibition, leaf senescence and mitophagy-the autophagic turnover of mitochondria in yeast and mammals.