Abstract
Chloroplasts are extraordinary organelles for photosynthesis and nutrient storage in plants. During leaf senescence or under stress conditions, damaged chloroplasts are degraded and provide nutrients for developing organs. Autophagy is a high-throughput degradation pathway for intracellular material turnover in eukaryotes. Along with chloroplast degradation, chlorophyll, an important component of the photosynthetic machine, is also degraded. However, the chlorophyll degradation pathways under high light intensity and high temperature stress are not well known. Here, we identified and characterized a novel Arabidopsis mutant, sl2 (seedling lethal 2), showing defective chloroplast development and accelerated chlorophyll degradation. Map-based cloning combined with high-throughput sequencing analysis revealed that a 118.6 kb deletion region was associated with the phenotype of the mutant. Complementary experiments confirmed that the loss of function of ATG2 was responsible for accelerating chlorophyll degradation in sl2 mutants. Furthermore, we analyzed chlorophyll degradation under abiotic stress conditions and found that both chloroplast vesiculation and autophagy take part in chlorophyll degradation under high light intensity and high temperature stress. These results enhanced our understanding of chlorophyll degradation under high light intensity and high temperature stress.
Highlights
Plants obtain energy for growth and development via photosynthesis and the oxidation of organic substrates by respiration [1]
The abundance of most of the PSII and cytochrome b6f complex proteins, including D1, D2, PsbO, PsbQ, LHCII, b6, and PetC, was decreased remarkably (Figure 1h). These results suggest that sl2 mutants suffer from chloroplast dysplasia in cotyledons and true leaves and from accelerated chlorophyll degradation and affected thylakoid proteins accumulation compared with WT plants, which lead to dramatic changes in the growth phenotype of sl2 mutants
autophagy-related 2 (ATG2) is a member of the autophagy family, known as a major system for clearing both surplus and dysfunctional organelles, and the mechanisms have been well elucidated in yeast and animals [49]
Summary
Plants obtain energy for growth and development via photosynthesis and the oxidation of organic substrates by respiration [1]. During senescence onset or under stress conditions, photosynthesis is severely affected, and plant cells recycle damaged organelles to release nutrients to improve survivability [2,3]. Chloroplasts are extraordinary organelles in photosynthetic plants and contain 80% of the nitrogen in leaves. During leaf senescence or under stress conditions, damaged chloroplasts are degraded and provide nutrients for new leaves or developing organs [4]. Chlorophylls, the most important natural pigments, combine with photosynthetic proteins to capture solar energy and transfer electrons. The dissociation of chlorophyll and its associated proteins is a necessary step for chloroplast degradation [5]
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