The core autophagy machinery is not required for chloroplast singlet oxygen-mediated cell death in the Arabidopsis thaliana plastid ferrochelatase two mutant

Journal Article · 18 July 2021 · BMC Plant Biology

DOI: https://doi.org/10.1186/s12870-021-03119-x · OSTI ID:1853360

Lemke, Matthew D.  ^[1]; Fisher, Karen E.  ^[2]; Kozlowska, Marta A.  ^[2]; Tano, David W.  ^[2]; Woodson, Jesse D.  ^[2]

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1. Univ. of Arizona, Tucson, AZ (United States). The School of Plant Sciences; Univ. of Arizona, Tucson, AZ (United States)
2. Univ. of Arizona, Tucson, AZ (United States). The School of Plant Sciences

Chloroplasts respond to stress and changes in the environment by producing reactive oxygen species (ROS) that have specific signaling abilities. The ROS singlet oxygen (¹O₂) is unique in that it can signal to initiate cellular degradation including the selective degradation of damaged chloroplasts. This chloroplast quality control pathway can be monitored in theArabidopsisthaliana mutantplastid ferrochelatase two(fc2) that conditionally accumulates chloroplast¹O₂under diurnal light cycling conditions leading to rapid chloroplast degradation and eventual cell death. The cellular machinery involved in such degradation, however, remains unknown. Recently, it was demonstrated that whole damaged chloroplasts can be transported to the central vacuole via a process requiring autophagosomes and core components of the autophagy machinery. The relationship between this process, referred to as chlorophagy, and the degradation of¹O₂-stressed chloroplasts and cells has remained unexplored. ResultsTo further understand¹O₂-induced cellular degradation and determine what role autophagy may play, the expression of autophagy-related genes was monitored in¹O₂-stressedfc2seedlings and found to be induced. Although autophagosomes were present infc2cells, they did not associate with chloroplasts during¹O₂stress. Mutations affecting the core autophagy machinery (atg5,atg7, andatg10) were unable to suppress¹O₂-induced cell death or chloroplast protrusion into the central vacuole, suggesting autophagosome formation is dispensable for such¹O₂–mediated cellular degradation. However, bothatg5andatg7led to specific defects in chloroplast ultrastructure and photosynthetic efficiencies, suggesting core autophagy machinery is involved in protecting chloroplasts from photo-oxidative damage. Finally, genes predicted to be involved in microautophagy were shown to be induced in stressedfc2seedlings, indicating a possible role for an alternate form of autophagy in the dismantling of¹O₂-damaged chloroplasts. ConclusionsOur results support the hypothesis that¹O₂-dependent cell death is independent from autophagosome formation, canonical autophagy, and chlorophagy. Furthermore, autophagosome-independent microautophagy may be involved in degrading¹O₂-damaged chloroplasts. At the same time, canonical autophagy may still play a role in protecting chloroplasts from¹O₂-induced photo-oxidative stress. Together, this suggests chloroplast function and degradation is a complex process utilizing multiple autophagy and degradation machineries, possibly depending on the type of stress or damage incurred.

• Research Organization: Univ. of Arizona, Tucson, AZ (United States)
• Sponsoring Organization: USDOE; USDOE Office of Science (SC)
• Grant/Contract Number: SC0019573
• OSTI ID: 1853360
• Journal Information: BMC Plant Biology, Journal Name: BMC Plant Biology Journal Issue: 1 Vol. 21; ISSN 1471-2229
• Publisher: BioMed CentralCopyright Statement
• Country of Publication: United States
• Language: English